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linux/arch/x86/kvm/mmu/paging_tmpl.h
Sean Christopherson 0e3223d8d0 KVM: x86/mmu: Use dummy root, backed by zero page, for !visible guest roots 
When attempting to allocate a shadow root for a !visible guest root gfn,
e.g. that resides in MMIO space, load a dummy root that is backed by the
zero page instead of immediately synthesizing a triple fault shutdown
(using the zero page ensures any attempt to translate memory will generate
a !PRESENT fault and thus VM-Exit).

Unless the vCPU is racing with memslot activity, KVM will inject a page
fault due to not finding a visible slot in FNAME(walk_addr_generic), i.e.
the end result is mostly same, but critically KVM will inject a fault only
*after* KVM runs the vCPU with the bogus root.

Waiting to inject a fault until after running the vCPU fixes a bug where
KVM would bail from nested VM-Enter if L1 tried to run L2 with TDP enabled
and a !visible root.  Even though a bad root will *probably* lead to
shutdown, (a) it's not guaranteed and (b) the CPU won't read the
underlying memory until after VM-Enter succeeds.  E.g. if L1 runs L2 with
a VMX preemption timer value of '0', then architecturally the preemption
timer VM-Exit is guaranteed to occur before the CPU executes any
instruction, i.e. before the CPU needs to translate a GPA to a HPA (so
long as there are no injected events with higher priority than the
preemption timer).

If KVM manages to get to FNAME(fetch) with a dummy root, e.g. because
userspace created a memslot between installing the dummy root and handling
the page fault, simply unload the MMU to allocate a new root and retry the
instruction.  Use KVM_REQ_MMU_FREE_OBSOLETE_ROOTS to drop the root, as
invoking kvm_mmu_free_roots() while holding mmu_lock would deadlock, and
conceptually the dummy root has indeeed become obsolete.  The only
difference versus existing usage of KVM_REQ_MMU_FREE_OBSOLETE_ROOTS is
that the root has become obsolete due to memslot *creation*, not memslot
deletion or movement.

Reported-by: Reima Ishii <ishiir@g.ecc.u-tokyo.ac.jp>
Cc: Yu Zhang <yu.c.zhang@linux.intel.com>
Link: https://lore.kernel.org/r/20230729005200.1057358-6-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2023-08-31 14:08:24 -04:00

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/* SPDX-License-Identifier: GPL-2.0-only */
/*
* Kernel-based Virtual Machine driver for Linux
*
* This module enables machines with Intel VT-x extensions to run virtual
* machines without emulation or binary translation.
*
* MMU support
*
* Copyright (C) 2006 Qumranet, Inc.
* Copyright 2010 Red Hat, Inc. and/or its affiliates.
*
* Authors:
* Yaniv Kamay <yaniv@qumranet.com>
* Avi Kivity <avi@qumranet.com>
*/
/*
* The MMU needs to be able to access/walk 32-bit and 64-bit guest page tables,
* as well as guest EPT tables, so the code in this file is compiled thrice,
* once per guest PTE type. The per-type defines are #undef'd at the end.
*/
#if PTTYPE == 64
#define pt_element_t u64
#define guest_walker guest_walker64
#define FNAME(name) paging##64_##name
#define PT_LEVEL_BITS 9
#define PT_GUEST_DIRTY_SHIFT PT_DIRTY_SHIFT
#define PT_GUEST_ACCESSED_SHIFT PT_ACCESSED_SHIFT
#define PT_HAVE_ACCESSED_DIRTY(mmu) true
#ifdef CONFIG_X86_64
#define PT_MAX_FULL_LEVELS PT64_ROOT_MAX_LEVEL
#else
#define PT_MAX_FULL_LEVELS 2
#endif
#elif PTTYPE == 32
#define pt_element_t u32
#define guest_walker guest_walker32
#define FNAME(name) paging##32_##name
#define PT_LEVEL_BITS 10
#define PT_MAX_FULL_LEVELS 2
#define PT_GUEST_DIRTY_SHIFT PT_DIRTY_SHIFT
#define PT_GUEST_ACCESSED_SHIFT PT_ACCESSED_SHIFT
#define PT_HAVE_ACCESSED_DIRTY(mmu) true
#define PT32_DIR_PSE36_SIZE 4
#define PT32_DIR_PSE36_SHIFT 13
#define PT32_DIR_PSE36_MASK \
(((1ULL << PT32_DIR_PSE36_SIZE) - 1) << PT32_DIR_PSE36_SHIFT)
#elif PTTYPE == PTTYPE_EPT
#define pt_element_t u64
#define guest_walker guest_walkerEPT
#define FNAME(name) ept_##name
#define PT_LEVEL_BITS 9
#define PT_GUEST_DIRTY_SHIFT 9
#define PT_GUEST_ACCESSED_SHIFT 8
#define PT_HAVE_ACCESSED_DIRTY(mmu) (!(mmu)->cpu_role.base.ad_disabled)
#define PT_MAX_FULL_LEVELS PT64_ROOT_MAX_LEVEL
#else
#error Invalid PTTYPE value
#endif
/* Common logic, but per-type values. These also need to be undefined. */
#define PT_BASE_ADDR_MASK ((pt_element_t)(((1ULL << 52) - 1) & ~(u64)(PAGE_SIZE-1)))
#define PT_LVL_ADDR_MASK(lvl) __PT_LVL_ADDR_MASK(PT_BASE_ADDR_MASK, lvl, PT_LEVEL_BITS)
#define PT_LVL_OFFSET_MASK(lvl) __PT_LVL_OFFSET_MASK(PT_BASE_ADDR_MASK, lvl, PT_LEVEL_BITS)
#define PT_INDEX(addr, lvl) __PT_INDEX(addr, lvl, PT_LEVEL_BITS)
#define PT_GUEST_DIRTY_MASK (1 << PT_GUEST_DIRTY_SHIFT)
#define PT_GUEST_ACCESSED_MASK (1 << PT_GUEST_ACCESSED_SHIFT)
#define gpte_to_gfn_lvl FNAME(gpte_to_gfn_lvl)
#define gpte_to_gfn(pte) gpte_to_gfn_lvl((pte), PG_LEVEL_4K)
/*
* The guest_walker structure emulates the behavior of the hardware page
* table walker.
*/
struct guest_walker {
int level;
unsigned max_level;
gfn_t table_gfn[PT_MAX_FULL_LEVELS];
pt_element_t ptes[PT_MAX_FULL_LEVELS];
pt_element_t prefetch_ptes[PTE_PREFETCH_NUM];
gpa_t pte_gpa[PT_MAX_FULL_LEVELS];
pt_element_t __user *ptep_user[PT_MAX_FULL_LEVELS];
bool pte_writable[PT_MAX_FULL_LEVELS];
unsigned int pt_access[PT_MAX_FULL_LEVELS];
unsigned int pte_access;
gfn_t gfn;
struct x86_exception fault;
};
#if PTTYPE == 32
static inline gfn_t pse36_gfn_delta(u32 gpte)
{
int shift = 32 - PT32_DIR_PSE36_SHIFT - PAGE_SHIFT;
return (gpte & PT32_DIR_PSE36_MASK) << shift;
}
#endif
static gfn_t gpte_to_gfn_lvl(pt_element_t gpte, int lvl)
{
return (gpte & PT_LVL_ADDR_MASK(lvl)) >> PAGE_SHIFT;
}
static inline void FNAME(protect_clean_gpte)(struct kvm_mmu *mmu, unsigned *access,
unsigned gpte)
{
unsigned mask;
/* dirty bit is not supported, so no need to track it */
if (!PT_HAVE_ACCESSED_DIRTY(mmu))
return;
BUILD_BUG_ON(PT_WRITABLE_MASK != ACC_WRITE_MASK);
mask = (unsigned)~ACC_WRITE_MASK;
/* Allow write access to dirty gptes */
mask |= (gpte >> (PT_GUEST_DIRTY_SHIFT - PT_WRITABLE_SHIFT)) &
PT_WRITABLE_MASK;
*access &= mask;
}
static inline int FNAME(is_present_gpte)(unsigned long pte)
{
#if PTTYPE != PTTYPE_EPT
return pte & PT_PRESENT_MASK;
#else
return pte & 7;
#endif
}
static bool FNAME(is_bad_mt_xwr)(struct rsvd_bits_validate *rsvd_check, u64 gpte)
{
#if PTTYPE != PTTYPE_EPT
return false;
#else
return __is_bad_mt_xwr(rsvd_check, gpte);
#endif
}
static bool FNAME(is_rsvd_bits_set)(struct kvm_mmu *mmu, u64 gpte, int level)
{
return __is_rsvd_bits_set(&mmu->guest_rsvd_check, gpte, level) ||
FNAME(is_bad_mt_xwr)(&mmu->guest_rsvd_check, gpte);
}
static bool FNAME(prefetch_invalid_gpte)(struct kvm_vcpu *vcpu,
struct kvm_mmu_page *sp, u64 *spte,
u64 gpte)
{
if (!FNAME(is_present_gpte)(gpte))
goto no_present;
/* Prefetch only accessed entries (unless A/D bits are disabled). */
if (PT_HAVE_ACCESSED_DIRTY(vcpu->arch.mmu) &&
!(gpte & PT_GUEST_ACCESSED_MASK))
goto no_present;
if (FNAME(is_rsvd_bits_set)(vcpu->arch.mmu, gpte, PG_LEVEL_4K))
goto no_present;
return false;
no_present:
drop_spte(vcpu->kvm, spte);
return true;
}
/*
* For PTTYPE_EPT, a page table can be executable but not readable
* on supported processors. Therefore, set_spte does not automatically
* set bit 0 if execute only is supported. Here, we repurpose ACC_USER_MASK
* to signify readability since it isn't used in the EPT case
*/
static inline unsigned FNAME(gpte_access)(u64 gpte)
{
unsigned access;
#if PTTYPE == PTTYPE_EPT
access = ((gpte & VMX_EPT_WRITABLE_MASK) ? ACC_WRITE_MASK : 0) |
((gpte & VMX_EPT_EXECUTABLE_MASK) ? ACC_EXEC_MASK : 0) |
((gpte & VMX_EPT_READABLE_MASK) ? ACC_USER_MASK : 0);
#else
BUILD_BUG_ON(ACC_EXEC_MASK != PT_PRESENT_MASK);
BUILD_BUG_ON(ACC_EXEC_MASK != 1);
access = gpte & (PT_WRITABLE_MASK | PT_USER_MASK | PT_PRESENT_MASK);
/* Combine NX with P (which is set here) to get ACC_EXEC_MASK. */
access ^= (gpte >> PT64_NX_SHIFT);
#endif
return access;
}
static int FNAME(update_accessed_dirty_bits)(struct kvm_vcpu *vcpu,
struct kvm_mmu *mmu,
struct guest_walker *walker,
gpa_t addr, int write_fault)
{
unsigned level, index;
pt_element_t pte, orig_pte;
pt_element_t __user *ptep_user;
gfn_t table_gfn;
int ret;
/* dirty/accessed bits are not supported, so no need to update them */
if (!PT_HAVE_ACCESSED_DIRTY(mmu))
return 0;
for (level = walker->max_level; level >= walker->level; --level) {
pte = orig_pte = walker->ptes[level - 1];
table_gfn = walker->table_gfn[level - 1];
ptep_user = walker->ptep_user[level - 1];
index = offset_in_page(ptep_user) / sizeof(pt_element_t);
if (!(pte & PT_GUEST_ACCESSED_MASK)) {
trace_kvm_mmu_set_accessed_bit(table_gfn, index, sizeof(pte));
pte |= PT_GUEST_ACCESSED_MASK;
}
if (level == walker->level && write_fault &&
!(pte & PT_GUEST_DIRTY_MASK)) {
trace_kvm_mmu_set_dirty_bit(table_gfn, index, sizeof(pte));
#if PTTYPE == PTTYPE_EPT
if (kvm_x86_ops.nested_ops->write_log_dirty(vcpu, addr))
return -EINVAL;
#endif
pte |= PT_GUEST_DIRTY_MASK;
}
if (pte == orig_pte)
continue;
/*
* If the slot is read-only, simply do not process the accessed
* and dirty bits. This is the correct thing to do if the slot
* is ROM, and page tables in read-as-ROM/write-as-MMIO slots
* are only supported if the accessed and dirty bits are already
* set in the ROM (so that MMIO writes are never needed).
*
* Note that NPT does not allow this at all and faults, since
* it always wants nested page table entries for the guest
* page tables to be writable. And EPT works but will simply
* overwrite the read-only memory to set the accessed and dirty
* bits.
*/
if (unlikely(!walker->pte_writable[level - 1]))
continue;
ret = __try_cmpxchg_user(ptep_user, &orig_pte, pte, fault);
if (ret)
return ret;
kvm_vcpu_mark_page_dirty(vcpu, table_gfn);
walker->ptes[level - 1] = pte;
}
return 0;
}
static inline unsigned FNAME(gpte_pkeys)(struct kvm_vcpu *vcpu, u64 gpte)
{
unsigned pkeys = 0;
#if PTTYPE == 64
pte_t pte = {.pte = gpte};
pkeys = pte_flags_pkey(pte_flags(pte));
#endif
return pkeys;
}
static inline bool FNAME(is_last_gpte)(struct kvm_mmu *mmu,
unsigned int level, unsigned int gpte)
{
/*
* For EPT and PAE paging (both variants), bit 7 is either reserved at
* all level or indicates a huge page (ignoring CR3/EPTP). In either
* case, bit 7 being set terminates the walk.
*/
#if PTTYPE == 32
/*
* 32-bit paging requires special handling because bit 7 is ignored if
* CR4.PSE=0, not reserved. Clear bit 7 in the gpte if the level is
* greater than the last level for which bit 7 is the PAGE_SIZE bit.
*
* The RHS has bit 7 set iff level < (2 + PSE). If it is clear, bit 7
* is not reserved and does not indicate a large page at this level,
* so clear PT_PAGE_SIZE_MASK in gpte if that is the case.
*/
gpte &= level - (PT32_ROOT_LEVEL + mmu->cpu_role.ext.cr4_pse);
#endif
/*
* PG_LEVEL_4K always terminates. The RHS has bit 7 set
* iff level <= PG_LEVEL_4K, which for our purpose means
* level == PG_LEVEL_4K; set PT_PAGE_SIZE_MASK in gpte then.
*/
gpte |= level - PG_LEVEL_4K - 1;
return gpte & PT_PAGE_SIZE_MASK;
}
/*
* Fetch a guest pte for a guest virtual address, or for an L2's GPA.
*/
static int FNAME(walk_addr_generic)(struct guest_walker *walker,
struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
gpa_t addr, u64 access)
{
int ret;
pt_element_t pte;
pt_element_t __user *ptep_user;
gfn_t table_gfn;
u64 pt_access, pte_access;
unsigned index, accessed_dirty, pte_pkey;
u64 nested_access;
gpa_t pte_gpa;
bool have_ad;
int offset;
u64 walk_nx_mask = 0;
const int write_fault = access & PFERR_WRITE_MASK;
const int user_fault = access & PFERR_USER_MASK;
const int fetch_fault = access & PFERR_FETCH_MASK;
u16 errcode = 0;
gpa_t real_gpa;
gfn_t gfn;
trace_kvm_mmu_pagetable_walk(addr, access);
retry_walk:
walker->level = mmu->cpu_role.base.level;
pte = kvm_mmu_get_guest_pgd(vcpu, mmu);
have_ad = PT_HAVE_ACCESSED_DIRTY(mmu);
#if PTTYPE == 64
walk_nx_mask = 1ULL << PT64_NX_SHIFT;
if (walker->level == PT32E_ROOT_LEVEL) {
pte = mmu->get_pdptr(vcpu, (addr >> 30) & 3);
trace_kvm_mmu_paging_element(pte, walker->level);
if (!FNAME(is_present_gpte)(pte))
goto error;
--walker->level;
}
#endif
walker->max_level = walker->level;
/*
* FIXME: on Intel processors, loads of the PDPTE registers for PAE paging
* by the MOV to CR instruction are treated as reads and do not cause the
* processor to set the dirty flag in any EPT paging-structure entry.
*/
nested_access = (have_ad ? PFERR_WRITE_MASK : 0) | PFERR_USER_MASK;
pte_access = ~0;
/*
* Queue a page fault for injection if this assertion fails, as callers
* assume that walker.fault contains sane info on a walk failure. I.e.
* avoid making the situation worse by inducing even worse badness
* between when the assertion fails and when KVM kicks the vCPU out to
* userspace (because the VM is bugged).
*/
if (KVM_BUG_ON(is_long_mode(vcpu) && !is_pae(vcpu), vcpu->kvm))
goto error;
++walker->level;
do {
struct kvm_memory_slot *slot;
unsigned long host_addr;
pt_access = pte_access;
--walker->level;
index = PT_INDEX(addr, walker->level);
table_gfn = gpte_to_gfn(pte);
offset = index * sizeof(pt_element_t);
pte_gpa = gfn_to_gpa(table_gfn) + offset;
BUG_ON(walker->level < 1);
walker->table_gfn[walker->level - 1] = table_gfn;
walker->pte_gpa[walker->level - 1] = pte_gpa;
real_gpa = kvm_translate_gpa(vcpu, mmu, gfn_to_gpa(table_gfn),
nested_access, &walker->fault);
/*
* FIXME: This can happen if emulation (for of an INS/OUTS
* instruction) triggers a nested page fault. The exit
* qualification / exit info field will incorrectly have
* "guest page access" as the nested page fault's cause,
* instead of "guest page structure access". To fix this,
* the x86_exception struct should be augmented with enough
* information to fix the exit_qualification or exit_info_1
* fields.
*/
if (unlikely(real_gpa == INVALID_GPA))
return 0;
slot = kvm_vcpu_gfn_to_memslot(vcpu, gpa_to_gfn(real_gpa));
if (!kvm_is_visible_memslot(slot))
goto error;
host_addr = gfn_to_hva_memslot_prot(slot, gpa_to_gfn(real_gpa),
&walker->pte_writable[walker->level - 1]);
if (unlikely(kvm_is_error_hva(host_addr)))
goto error;
ptep_user = (pt_element_t __user *)((void *)host_addr + offset);
if (unlikely(__get_user(pte, ptep_user)))
goto error;
walker->ptep_user[walker->level - 1] = ptep_user;
trace_kvm_mmu_paging_element(pte, walker->level);
/*
* Inverting the NX it lets us AND it like other
* permission bits.
*/
pte_access = pt_access & (pte ^ walk_nx_mask);
if (unlikely(!FNAME(is_present_gpte)(pte)))
goto error;
if (unlikely(FNAME(is_rsvd_bits_set)(mmu, pte, walker->level))) {
errcode = PFERR_RSVD_MASK | PFERR_PRESENT_MASK;
goto error;
}
walker->ptes[walker->level - 1] = pte;
/* Convert to ACC_*_MASK flags for struct guest_walker. */
walker->pt_access[walker->level - 1] = FNAME(gpte_access)(pt_access ^ walk_nx_mask);
} while (!FNAME(is_last_gpte)(mmu, walker->level, pte));
pte_pkey = FNAME(gpte_pkeys)(vcpu, pte);
accessed_dirty = have_ad ? pte_access & PT_GUEST_ACCESSED_MASK : 0;
/* Convert to ACC_*_MASK flags for struct guest_walker. */
walker->pte_access = FNAME(gpte_access)(pte_access ^ walk_nx_mask);
errcode = permission_fault(vcpu, mmu, walker->pte_access, pte_pkey, access);
if (unlikely(errcode))
goto error;
gfn = gpte_to_gfn_lvl(pte, walker->level);
gfn += (addr & PT_LVL_OFFSET_MASK(walker->level)) >> PAGE_SHIFT;
#if PTTYPE == 32
if (walker->level > PG_LEVEL_4K && is_cpuid_PSE36())
gfn += pse36_gfn_delta(pte);
#endif
real_gpa = kvm_translate_gpa(vcpu, mmu, gfn_to_gpa(gfn), access, &walker->fault);
if (real_gpa == INVALID_GPA)
return 0;
walker->gfn = real_gpa >> PAGE_SHIFT;
if (!write_fault)
FNAME(protect_clean_gpte)(mmu, &walker->pte_access, pte);
else
/*
* On a write fault, fold the dirty bit into accessed_dirty.
* For modes without A/D bits support accessed_dirty will be
* always clear.
*/
accessed_dirty &= pte >>
(PT_GUEST_DIRTY_SHIFT - PT_GUEST_ACCESSED_SHIFT);
if (unlikely(!accessed_dirty)) {
ret = FNAME(update_accessed_dirty_bits)(vcpu, mmu, walker,
addr, write_fault);
if (unlikely(ret < 0))
goto error;
else if (ret)
goto retry_walk;
}
return 1;
error:
errcode |= write_fault | user_fault;
if (fetch_fault && (is_efer_nx(mmu) || is_cr4_smep(mmu)))
errcode |= PFERR_FETCH_MASK;
walker->fault.vector = PF_VECTOR;
walker->fault.error_code_valid = true;
walker->fault.error_code = errcode;
#if PTTYPE == PTTYPE_EPT
/*
* Use PFERR_RSVD_MASK in error_code to tell if EPT
* misconfiguration requires to be injected. The detection is
* done by is_rsvd_bits_set() above.
*
* We set up the value of exit_qualification to inject:
* [2:0] - Derive from the access bits. The exit_qualification might be
* out of date if it is serving an EPT misconfiguration.
* [5:3] - Calculated by the page walk of the guest EPT page tables
* [7:8] - Derived from [7:8] of real exit_qualification
*
* The other bits are set to 0.
*/
if (!(errcode & PFERR_RSVD_MASK)) {
vcpu->arch.exit_qualification &= (EPT_VIOLATION_GVA_IS_VALID |
EPT_VIOLATION_GVA_TRANSLATED);
if (write_fault)
vcpu->arch.exit_qualification |= EPT_VIOLATION_ACC_WRITE;
if (user_fault)
vcpu->arch.exit_qualification |= EPT_VIOLATION_ACC_READ;
if (fetch_fault)
vcpu->arch.exit_qualification |= EPT_VIOLATION_ACC_INSTR;
/*
* Note, pte_access holds the raw RWX bits from the EPTE, not
* ACC_*_MASK flags!
*/
vcpu->arch.exit_qualification |= (pte_access & VMX_EPT_RWX_MASK) <<
EPT_VIOLATION_RWX_SHIFT;
}
#endif
walker->fault.address = addr;
walker->fault.nested_page_fault = mmu != vcpu->arch.walk_mmu;
walker->fault.async_page_fault = false;
trace_kvm_mmu_walker_error(walker->fault.error_code);
return 0;
}
static int FNAME(walk_addr)(struct guest_walker *walker,
struct kvm_vcpu *vcpu, gpa_t addr, u64 access)
{
return FNAME(walk_addr_generic)(walker, vcpu, vcpu->arch.mmu, addr,
access);
}
static bool
FNAME(prefetch_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
u64 *spte, pt_element_t gpte)
{
struct kvm_memory_slot *slot;
unsigned pte_access;
gfn_t gfn;
kvm_pfn_t pfn;
if (FNAME(prefetch_invalid_gpte)(vcpu, sp, spte, gpte))
return false;
gfn = gpte_to_gfn(gpte);
pte_access = sp->role.access & FNAME(gpte_access)(gpte);
FNAME(protect_clean_gpte)(vcpu->arch.mmu, &pte_access, gpte);
slot = gfn_to_memslot_dirty_bitmap(vcpu, gfn, pte_access & ACC_WRITE_MASK);
if (!slot)
return false;
pfn = gfn_to_pfn_memslot_atomic(slot, gfn);
if (is_error_pfn(pfn))
return false;
mmu_set_spte(vcpu, slot, spte, pte_access, gfn, pfn, NULL);
kvm_release_pfn_clean(pfn);
return true;
}
static bool FNAME(gpte_changed)(struct kvm_vcpu *vcpu,
struct guest_walker *gw, int level)
{
pt_element_t curr_pte;
gpa_t base_gpa, pte_gpa = gw->pte_gpa[level - 1];
u64 mask;
int r, index;
if (level == PG_LEVEL_4K) {
mask = PTE_PREFETCH_NUM * sizeof(pt_element_t) - 1;
base_gpa = pte_gpa & ~mask;
index = (pte_gpa - base_gpa) / sizeof(pt_element_t);
r = kvm_vcpu_read_guest_atomic(vcpu, base_gpa,
gw->prefetch_ptes, sizeof(gw->prefetch_ptes));
curr_pte = gw->prefetch_ptes[index];
} else
r = kvm_vcpu_read_guest_atomic(vcpu, pte_gpa,
&curr_pte, sizeof(curr_pte));
return r || curr_pte != gw->ptes[level - 1];
}
static void FNAME(pte_prefetch)(struct kvm_vcpu *vcpu, struct guest_walker *gw,
u64 *sptep)
{
struct kvm_mmu_page *sp;
pt_element_t *gptep = gw->prefetch_ptes;
u64 *spte;
int i;
sp = sptep_to_sp(sptep);
if (sp->role.level > PG_LEVEL_4K)
return;
/*
* If addresses are being invalidated, skip prefetching to avoid
* accidentally prefetching those addresses.
*/
if (unlikely(vcpu->kvm->mmu_invalidate_in_progress))
return;
if (sp->role.direct)
return __direct_pte_prefetch(vcpu, sp, sptep);
i = spte_index(sptep) & ~(PTE_PREFETCH_NUM - 1);
spte = sp->spt + i;
for (i = 0; i < PTE_PREFETCH_NUM; i++, spte++) {
if (spte == sptep)
continue;
if (is_shadow_present_pte(*spte))
continue;
if (!FNAME(prefetch_gpte)(vcpu, sp, spte, gptep[i]))
break;
}
}
/*
* Fetch a shadow pte for a specific level in the paging hierarchy.
* If the guest tries to write a write-protected page, we need to
* emulate this operation, return 1 to indicate this case.
*/
static int FNAME(fetch)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
struct guest_walker *gw)
{
struct kvm_mmu_page *sp = NULL;
struct kvm_shadow_walk_iterator it;
unsigned int direct_access, access;
int top_level, ret;
gfn_t base_gfn = fault->gfn;
WARN_ON_ONCE(gw->gfn != base_gfn);
direct_access = gw->pte_access;
top_level = vcpu->arch.mmu->cpu_role.base.level;
if (top_level == PT32E_ROOT_LEVEL)
top_level = PT32_ROOT_LEVEL;
/*
* Verify that the top-level gpte is still there. Since the page
* is a root page, it is either write protected (and cannot be
* changed from now on) or it is invalid (in which case, we don't
* really care if it changes underneath us after this point).
*/
if (FNAME(gpte_changed)(vcpu, gw, top_level))
goto out_gpte_changed;
if (WARN_ON_ONCE(!VALID_PAGE(vcpu->arch.mmu->root.hpa)))
goto out_gpte_changed;
/*
* Load a new root and retry the faulting instruction in the extremely
* unlikely scenario that the guest root gfn became visible between
* loading a dummy root and handling the resulting page fault, e.g. if
* userspace create a memslot in the interim.
*/
if (unlikely(kvm_mmu_is_dummy_root(vcpu->arch.mmu->root.hpa))) {
kvm_make_request(KVM_REQ_MMU_FREE_OBSOLETE_ROOTS, vcpu);
goto out_gpte_changed;
}
for_each_shadow_entry(vcpu, fault->addr, it) {
gfn_t table_gfn;
clear_sp_write_flooding_count(it.sptep);
if (it.level == gw->level)
break;
table_gfn = gw->table_gfn[it.level - 2];
access = gw->pt_access[it.level - 2];
sp = kvm_mmu_get_child_sp(vcpu, it.sptep, table_gfn,
false, access);
if (sp != ERR_PTR(-EEXIST)) {
/*
* We must synchronize the pagetable before linking it
* because the guest doesn't need to flush tlb when
* the gpte is changed from non-present to present.
* Otherwise, the guest may use the wrong mapping.
*
* For PG_LEVEL_4K, kvm_mmu_get_page() has already
* synchronized it transiently via kvm_sync_page().
*
* For higher level pagetable, we synchronize it via
* the slower mmu_sync_children(). If it needs to
* break, some progress has been made; return
* RET_PF_RETRY and retry on the next #PF.
* KVM_REQ_MMU_SYNC is not necessary but it
* expedites the process.
*/
if (sp->unsync_children &&
mmu_sync_children(vcpu, sp, false))
return RET_PF_RETRY;
}
/*
* Verify that the gpte in the page we've just write
* protected is still there.
*/
if (FNAME(gpte_changed)(vcpu, gw, it.level - 1))
goto out_gpte_changed;
if (sp != ERR_PTR(-EEXIST))
link_shadow_page(vcpu, it.sptep, sp);
if (fault->write && table_gfn == fault->gfn)
fault->write_fault_to_shadow_pgtable = true;
}
/*
* Adjust the hugepage size _after_ resolving indirect shadow pages.
* KVM doesn't support mapping hugepages into the guest for gfns that
* are being shadowed by KVM, i.e. allocating a new shadow page may
* affect the allowed hugepage size.
*/
kvm_mmu_hugepage_adjust(vcpu, fault);
trace_kvm_mmu_spte_requested(fault);
for (; shadow_walk_okay(&it); shadow_walk_next(&it)) {
/*
* We cannot overwrite existing page tables with an NX
* large page, as the leaf could be executable.
*/
if (fault->nx_huge_page_workaround_enabled)
disallowed_hugepage_adjust(fault, *it.sptep, it.level);
base_gfn = gfn_round_for_level(fault->gfn, it.level);
if (it.level == fault->goal_level)
break;
validate_direct_spte(vcpu, it.sptep, direct_access);
sp = kvm_mmu_get_child_sp(vcpu, it.sptep, base_gfn,
true, direct_access);
if (sp == ERR_PTR(-EEXIST))
continue;
link_shadow_page(vcpu, it.sptep, sp);
if (fault->huge_page_disallowed)
account_nx_huge_page(vcpu->kvm, sp,
fault->req_level >= it.level);
}
if (WARN_ON_ONCE(it.level != fault->goal_level))
return -EFAULT;
ret = mmu_set_spte(vcpu, fault->slot, it.sptep, gw->pte_access,
base_gfn, fault->pfn, fault);
if (ret == RET_PF_SPURIOUS)
return ret;
FNAME(pte_prefetch)(vcpu, gw, it.sptep);
return ret;
out_gpte_changed:
return RET_PF_RETRY;
}
/*
* Page fault handler. There are several causes for a page fault:
* - there is no shadow pte for the guest pte
* - write access through a shadow pte marked read only so that we can set
* the dirty bit
* - write access to a shadow pte marked read only so we can update the page
* dirty bitmap, when userspace requests it
* - mmio access; in this case we will never install a present shadow pte
* - normal guest page fault due to the guest pte marked not present, not
* writable, or not executable
*
* Returns: 1 if we need to emulate the instruction, 0 otherwise, or
* a negative value on error.
*/
static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
{
struct guest_walker walker;
int r;
WARN_ON_ONCE(fault->is_tdp);
/*
* Look up the guest pte for the faulting address.
* If PFEC.RSVD is set, this is a shadow page fault.
* The bit needs to be cleared before walking guest page tables.
*/
r = FNAME(walk_addr)(&walker, vcpu, fault->addr,
fault->error_code & ~PFERR_RSVD_MASK);
/*
* The page is not mapped by the guest. Let the guest handle it.
*/
if (!r) {
if (!fault->prefetch)
kvm_inject_emulated_page_fault(vcpu, &walker.fault);
return RET_PF_RETRY;
}
fault->gfn = walker.gfn;
fault->max_level = walker.level;
fault->slot = kvm_vcpu_gfn_to_memslot(vcpu, fault->gfn);
if (page_fault_handle_page_track(vcpu, fault)) {
shadow_page_table_clear_flood(vcpu, fault->addr);
return RET_PF_EMULATE;
}
r = mmu_topup_memory_caches(vcpu, true);
if (r)
return r;
r = kvm_faultin_pfn(vcpu, fault, walker.pte_access);
if (r != RET_PF_CONTINUE)
return r;
/*
* Do not change pte_access if the pfn is a mmio page, otherwise
* we will cache the incorrect access into mmio spte.
*/
if (fault->write && !(walker.pte_access & ACC_WRITE_MASK) &&
!is_cr0_wp(vcpu->arch.mmu) && !fault->user && fault->slot) {
walker.pte_access |= ACC_WRITE_MASK;
walker.pte_access &= ~ACC_USER_MASK;
/*
* If we converted a user page to a kernel page,
* so that the kernel can write to it when cr0.wp=0,
* then we should prevent the kernel from executing it
* if SMEP is enabled.
*/
if (is_cr4_smep(vcpu->arch.mmu))
walker.pte_access &= ~ACC_EXEC_MASK;
}
r = RET_PF_RETRY;
write_lock(&vcpu->kvm->mmu_lock);
if (is_page_fault_stale(vcpu, fault))
goto out_unlock;
r = make_mmu_pages_available(vcpu);
if (r)
goto out_unlock;
r = FNAME(fetch)(vcpu, fault, &walker);
out_unlock:
write_unlock(&vcpu->kvm->mmu_lock);
kvm_release_pfn_clean(fault->pfn);
return r;
}
static gpa_t FNAME(get_level1_sp_gpa)(struct kvm_mmu_page *sp)
{
int offset = 0;
WARN_ON_ONCE(sp->role.level != PG_LEVEL_4K);
if (PTTYPE == 32)
offset = sp->role.quadrant << SPTE_LEVEL_BITS;
return gfn_to_gpa(sp->gfn) + offset * sizeof(pt_element_t);
}
/* Note, @addr is a GPA when gva_to_gpa() translates an L2 GPA to an L1 GPA. */
static gpa_t FNAME(gva_to_gpa)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
gpa_t addr, u64 access,
struct x86_exception *exception)
{
struct guest_walker walker;
gpa_t gpa = INVALID_GPA;
int r;
#ifndef CONFIG_X86_64
/* A 64-bit GVA should be impossible on 32-bit KVM. */
WARN_ON_ONCE((addr >> 32) && mmu == vcpu->arch.walk_mmu);
#endif
r = FNAME(walk_addr_generic)(&walker, vcpu, mmu, addr, access);
if (r) {
gpa = gfn_to_gpa(walker.gfn);
gpa |= addr & ~PAGE_MASK;
} else if (exception)
*exception = walker.fault;
return gpa;
}
/*
* Using the information in sp->shadowed_translation (kvm_mmu_page_get_gfn()) is
* safe because:
* - The spte has a reference to the struct page, so the pfn for a given gfn
* can't change unless all sptes pointing to it are nuked first.
*
* Returns
* < 0: failed to sync spte
* 0: the spte is synced and no tlb flushing is required
* > 0: the spte is synced and tlb flushing is required
*/
static int FNAME(sync_spte)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp, int i)
{
bool host_writable;
gpa_t first_pte_gpa;
u64 *sptep, spte;
struct kvm_memory_slot *slot;
unsigned pte_access;
pt_element_t gpte;
gpa_t pte_gpa;
gfn_t gfn;
if (WARN_ON_ONCE(!sp->spt[i]))
return 0;
first_pte_gpa = FNAME(get_level1_sp_gpa)(sp);
pte_gpa = first_pte_gpa + i * sizeof(pt_element_t);
if (kvm_vcpu_read_guest_atomic(vcpu, pte_gpa, &gpte,
sizeof(pt_element_t)))
return -1;
if (FNAME(prefetch_invalid_gpte)(vcpu, sp, &sp->spt[i], gpte))
return 1;
gfn = gpte_to_gfn(gpte);
pte_access = sp->role.access;
pte_access &= FNAME(gpte_access)(gpte);
FNAME(protect_clean_gpte)(vcpu->arch.mmu, &pte_access, gpte);
if (sync_mmio_spte(vcpu, &sp->spt[i], gfn, pte_access))
return 0;
/*
* Drop the SPTE if the new protections would result in a RWX=0
* SPTE or if the gfn is changing. The RWX=0 case only affects
* EPT with execute-only support, i.e. EPT without an effective
* "present" bit, as all other paging modes will create a
* read-only SPTE if pte_access is zero.
*/
if ((!pte_access && !shadow_present_mask) ||
gfn != kvm_mmu_page_get_gfn(sp, i)) {
drop_spte(vcpu->kvm, &sp->spt[i]);
return 1;
}
/*
* Do nothing if the permissions are unchanged. The existing SPTE is
* still, and prefetch_invalid_gpte() has verified that the A/D bits
* are set in the "new" gPTE, i.e. there is no danger of missing an A/D
* update due to A/D bits being set in the SPTE but not the gPTE.
*/
if (kvm_mmu_page_get_access(sp, i) == pte_access)
return 0;
/* Update the shadowed access bits in case they changed. */
kvm_mmu_page_set_access(sp, i, pte_access);
sptep = &sp->spt[i];
spte = *sptep;
host_writable = spte & shadow_host_writable_mask;
slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
make_spte(vcpu, sp, slot, pte_access, gfn,
spte_to_pfn(spte), spte, true, false,
host_writable, &spte);
return mmu_spte_update(sptep, spte);
}
#undef pt_element_t
#undef guest_walker
#undef FNAME
#undef PT_BASE_ADDR_MASK
#undef PT_INDEX
#undef PT_LVL_ADDR_MASK
#undef PT_LVL_OFFSET_MASK
#undef PT_LEVEL_BITS
#undef PT_MAX_FULL_LEVELS
#undef gpte_to_gfn
#undef gpte_to_gfn_lvl
#undef PT_GUEST_ACCESSED_MASK
#undef PT_GUEST_DIRTY_MASK
#undef PT_GUEST_DIRTY_SHIFT
#undef PT_GUEST_ACCESSED_SHIFT
#undef PT_HAVE_ACCESSED_DIRTY
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