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KVM: VMX: Retry APIC-access page reload if invalidation is in-progress

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Re-request an APIC-access page reload if there is a relevant mmu_notifier
invalidation in-progress when KVM retrieves the backing pfn, i.e. stall
vCPUs until the backing pfn for the APIC-access page is "officially"
stable.  Relying on the primary MMU to not make changes after invoking
->invalidate_range() works, e.g. any additional changes to a PRESENT PTE
would also trigger an ->invalidate_range(), but using ->invalidate_range()
to fudge around KVM not honoring past and in-progress invalidations is a
bit hacky.

Honoring invalidations will allow using KVM's standard mmu_notifier hooks
to detect APIC-access page reloads, which will in turn allow removing
KVM's implementation of ->invalidate_range() (the APIC-access page case is
a true one-off).

Opportunistically add a comment to explain why doing nothing if a memslot
isn't found is functionally correct.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lore.kernel.org/r/20230602011518.787006-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2023-06-01 18:15:16 -07:00
parent c3a1e119a3
commit 878940b33d
1 changed files with 45 additions and 5 deletions
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50
arch/x86/kvm/vmx/vmx.c
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@ -6714,7 +6714,12 @@ void vmx_set_virtual_apic_mode(struct kvm_vcpu *vcpu)
static void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu)
{
struct page *page;
const gfn_t gfn = APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT;
struct kvm *kvm = vcpu->kvm;
struct kvm_memslots *slots = kvm_memslots(kvm);
struct kvm_memory_slot *slot;
unsigned long mmu_seq;
kvm_pfn_t pfn;
/* Defer reload until vmcs01 is the current VMCS. */
if (is_guest_mode(vcpu)) {
@ -6726,18 +6731,53 @@ static void vmx_set_apic_access_page_addr(struct kvm_vcpu *vcpu)
SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES))
return;
page = gfn_to_page(vcpu->kvm, APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT);
if (is_error_page(page))
/*
* Grab the memslot so that the hva lookup for the mmu_notifier retry
* is guaranteed to use the same memslot as the pfn lookup, i.e. rely
* on the pfn lookup's validation of the memslot to ensure a valid hva
* is used for the retry check.
*/
slot = id_to_memslot(slots, APIC_ACCESS_PAGE_PRIVATE_MEMSLOT);
if (!slot || slot->flags & KVM_MEMSLOT_INVALID)
return;
vmcs_write64(APIC_ACCESS_ADDR, page_to_phys(page));
/*
* Ensure that the mmu_notifier sequence count is read before KVM
* retrieves the pfn from the primary MMU. Note, the memslot is
* protected by SRCU, not the mmu_notifier. Pairs with the smp_wmb()
* in kvm_mmu_invalidate_end().
*/
mmu_seq = kvm->mmu_invalidate_seq;
smp_rmb();
/*
* No need to retry if the memslot does not exist or is invalid. KVM
* controls the APIC-access page memslot, and only deletes the memslot
* if APICv is permanently inhibited, i.e. the memslot won't reappear.
*/
pfn = gfn_to_pfn_memslot(slot, gfn);
if (is_error_noslot_pfn(pfn))
return;
read_lock(&vcpu->kvm->mmu_lock);
if (mmu_invalidate_retry_hva(kvm, mmu_seq,
gfn_to_hva_memslot(slot, gfn))) {
kvm_make_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu);
read_unlock(&vcpu->kvm->mmu_lock);
goto out;
}
vmcs_write64(APIC_ACCESS_ADDR, pfn_to_hpa(pfn));
read_unlock(&vcpu->kvm->mmu_lock);
vmx_flush_tlb_current(vcpu);
out:
/*
* Do not pin apic access page in memory, the MMU notifier
* will call us again if it is migrated or swapped out.
*/
put_page(page);
kvm_release_pfn_clean(pfn);
}
static void vmx_hwapic_isr_update(int max_isr)