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KVM: x86: Reduce the number of emulator GPRs to '8' for 32-bit KVM

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Reduce the number of GPRs emulated by 32-bit KVM from 16 to 8.  KVM does
not support emulating 64-bit mode on 32-bit host kernels, and so should
never generate accesses to R8-15.

Opportunistically use NR_EMULATOR_GPRS in rsm_load_state_{32,64}() now
that it is precise and accurate for both flavors.

Wrap the definition with full #ifdef ugliness; sadly, IS_ENABLED()
doesn't guarantee a compile-time constant as far as BUILD_BUG_ON() is
concerned.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Message-Id: <20220526210817.3428868-6-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2022-05-26 21:08:14 +00:00 committed by Paolo Bonzini
parent 0cbc60d44c
commit b443183a25
2 changed files with 6 additions and 5 deletions
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4
arch/x86/kvm/emulate.c
View File

@ -2441,7 +2441,7 @@ static int rsm_load_state_32(struct x86_emulate_ctxt *ctxt,
ctxt->eflags = GET_SMSTATE(u32, smstate, 0x7ff4) | X86_EFLAGS_FIXED;
ctxt->_eip = GET_SMSTATE(u32, smstate, 0x7ff0);
for (i = 0; i < 8; i++)
for (i = 0; i < NR_EMULATOR_GPRS; i++)
*reg_write(ctxt, i) = GET_SMSTATE(u32, smstate, 0x7fd0 + i * 4);
val = GET_SMSTATE(u32, smstate, 0x7fcc);
@ -2498,7 +2498,7 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt,
u16 selector;
int i, r;
for (i = 0; i < 16; i++)
for (i = 0; i < NR_EMULATOR_GPRS; i++)
*reg_write(ctxt, i) = GET_SMSTATE(u64, smstate, 0x7ff8 - i * 8);
ctxt->_eip = GET_SMSTATE(u64, smstate, 0x7f78);

7
arch/x86/kvm/kvm_emulate.h
View File

@ -306,11 +306,12 @@ typedef void (*fastop_t)(struct fastop *);
* tracked/accessed via _eip, and except for RIP relative addressing, which
* also uses _eip, RIP cannot be a register operand nor can it be an operand in
* a ModRM or SIB byte.
*
* TODO: this is technically wrong for 32-bit KVM, which only supports 8 GPRs;
* R8-R15 don't exist.
*/
#ifdef CONFIG_X86_64
#define NR_EMULATOR_GPRS 16
#else
#define NR_EMULATOR_GPRS 8
#endif
struct x86_emulate_ctxt {
void *vcpu;