linux-kernel - [PATCH v4 5/7] x86: KVM: svm: remove hardcoded instruction length from intercepts

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Date:   Tue, 13 Aug 2019 15:53:33 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Jim Mattson <jmattson@...gle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: [PATCH v4 5/7] x86: KVM: svm: remove hardcoded instruction length from intercepts

Various intercepts hard-code the respective instruction lengths to optimize
skip_emulated_instruction(): when next_rip is pre-set we skip
kvm_emulate_instruction(vcpu, EMULTYPE_SKIP). The optimization is, however,
incorrect: different (redundant) prefixes could be used to enlarge the
instruction. We can't really avoid decoding.

svm->next_rip is not used when CPU supports 'nrips' (X86_FEATURE_NRIPS)
feature: next RIP is provided in VMCB. The feature is not really new
(Opteron G3s had it already) and the change should have zero affect.

Remove manual svm->next_rip setting with hard-coded instruction lengths.
The only case where we now use svm->next_rip is EXIT_IOIO: the instruction
length is provided to us by hardware.

Hardcoded RIP advancement remains in vmrun_interception(), this is going to
be taken care of separately.

Reported-by: Jim Mattson <jmattson@...gle.com>
Reviewed-by: Sean Christopherson <sean.j.christopherson@...el.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/svm.c | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 858feeac01a4..6d16d1898810 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -2903,13 +2903,11 @@ static int nop_on_interception(struct vcpu_svm *svm)
 
 static int halt_interception(struct vcpu_svm *svm)
 {
-	svm->next_rip = kvm_rip_read(&svm->vcpu) + 1;
 	return kvm_emulate_halt(&svm->vcpu);
 }
 
 static int vmmcall_interception(struct vcpu_svm *svm)
 {
-	svm->next_rip = kvm_rip_read(&svm->vcpu) + 3;
 	return kvm_emulate_hypercall(&svm->vcpu);
 }
 
@@ -3697,7 +3695,6 @@ static int vmload_interception(struct vcpu_svm *svm)
 
 	nested_vmcb = map.hva;
 
-	svm->next_rip = kvm_rip_read(&svm->vcpu) + 3;
 	ret = kvm_skip_emulated_instruction(&svm->vcpu);
 
 	nested_svm_vmloadsave(nested_vmcb, svm->vmcb);
@@ -3724,7 +3721,6 @@ static int vmsave_interception(struct vcpu_svm *svm)
 
 	nested_vmcb = map.hva;
 
-	svm->next_rip = kvm_rip_read(&svm->vcpu) + 3;
 	ret = kvm_skip_emulated_instruction(&svm->vcpu);
 
 	nested_svm_vmloadsave(svm->vmcb, nested_vmcb);
@@ -3775,7 +3771,6 @@ static int stgi_interception(struct vcpu_svm *svm)
 	if (vgif_enabled(svm))
 		clr_intercept(svm, INTERCEPT_STGI);
 
-	svm->next_rip = kvm_rip_read(&svm->vcpu) + 3;
 	ret = kvm_skip_emulated_instruction(&svm->vcpu);
 	kvm_make_request(KVM_REQ_EVENT, &svm->vcpu);
 
@@ -3791,7 +3786,6 @@ static int clgi_interception(struct vcpu_svm *svm)
 	if (nested_svm_check_permissions(svm))
 		return 1;
 
-	svm->next_rip = kvm_rip_read(&svm->vcpu) + 3;
 	ret = kvm_skip_emulated_instruction(&svm->vcpu);
 
 	disable_gif(svm);
@@ -3816,7 +3810,6 @@ static int invlpga_interception(struct vcpu_svm *svm)
 	/* Let's treat INVLPGA the same as INVLPG (can be optimized!) */
 	kvm_mmu_invlpg(vcpu, kvm_rax_read(&svm->vcpu));
 
-	svm->next_rip = kvm_rip_read(&svm->vcpu) + 3;
 	return kvm_skip_emulated_instruction(&svm->vcpu);
 }
 
@@ -3839,7 +3832,6 @@ static int xsetbv_interception(struct vcpu_svm *svm)
 	u32 index = kvm_rcx_read(&svm->vcpu);
 
 	if (kvm_set_xcr(&svm->vcpu, index, new_bv) == 0) {
-		svm->next_rip = kvm_rip_read(&svm->vcpu) + 3;
 		return kvm_skip_emulated_instruction(&svm->vcpu);
 	}
 
@@ -3921,7 +3913,6 @@ static int task_switch_interception(struct vcpu_svm *svm)
 
 static int cpuid_interception(struct vcpu_svm *svm)
 {
-	svm->next_rip = kvm_rip_read(&svm->vcpu) + 2;
 	return kvm_emulate_cpuid(&svm->vcpu);
 }
 
@@ -4251,7 +4242,6 @@ static int rdmsr_interception(struct vcpu_svm *svm)
 
 		kvm_rax_write(&svm->vcpu, msr_info.data & 0xffffffff);
 		kvm_rdx_write(&svm->vcpu, msr_info.data >> 32);
-		svm->next_rip = kvm_rip_read(&svm->vcpu) + 2;
 		return kvm_skip_emulated_instruction(&svm->vcpu);
 	}
 }
@@ -4457,7 +4447,6 @@ static int wrmsr_interception(struct vcpu_svm *svm)
 		return 1;
 	} else {
 		trace_kvm_msr_write(ecx, data);
-		svm->next_rip = kvm_rip_read(&svm->vcpu) + 2;
 		return kvm_skip_emulated_instruction(&svm->vcpu);
 	}
 }
-- 
2.20.1