linux-kernel - [PATCH 06/22] KVM: x86: Get RIP from vCPU state when storing it to last_retry

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Message-ID: <20240809190319.1710470-7-seanjc@google.com>
Date: Fri,  9 Aug 2024 12:03:03 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Peter Gonda <pgonda@...gle.com>, Michael Roth <michael.roth@....com>, 
	Vishal Annapurve <vannapurve@...gle.com>, Ackerly Tng <ackerleytng@...gle.com>
Subject: [PATCH 06/22] KVM: x86: Get RIP from vCPU state when storing it to last_retry_eip

Read RIP from vCPU state instead of pulling it from the emulation context
when filling last_retry_eip, which is part of the anti-infinite-loop
protection used when unprotecting and retrying instructions that hit a
write-protected gfn.

This will allow reusing the anti-infinite-loop protection in flows that
never make it into the emulator.

This is a glorified nop as ctxt->eip is set to kvm_rip_read() in
init_emulate_ctxt(), and EMULTYPE_PF emulation is mutually exclusive with
EMULTYPE_NO_DECODE and EMULTYPE_SKIP, i.e. always goes through
x86_decode_emulated_instruction() and hasn't advanced ctxt->eip (yet).

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/x86.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 2072cceac68f..372ed3842732 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8973,7 +8973,7 @@ static bool retry_instruction(struct x86_emulate_ctxt *ctxt,
 	if (!kvm_mmu_unprotect_page(vcpu->kvm, gpa_to_gfn(gpa)))
 		return false;

-	vcpu->arch.last_retry_eip = ctxt->eip;
+	vcpu->arch.last_retry_eip = kvm_rip_read(vcpu);
 	vcpu->arch.last_retry_addr = cr2_or_gpa;
 	return true;
 }
-- 
2.46.0.76.ge559c4bf1a-goog