[PATCH 5/5] x86: KVM: svm: remove hardcoded instruction length from intercepts

[Vitaly Kuznetsov]

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.

Reported-by: Jim Mattson <jmatt...@google.com>
Signed-off-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
---
 arch/x86/kvm/svm.c | 15 ++-------------
 1 file changed, 2 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index f0e7e1b1c017..c6aa66324326 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -2907,13 +2907,11 @@ 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);
 }
 
@@ -3701,7 +3699,6 @@ 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);
@@ -3728,7 +3725,6 @@ 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);
@@ -3742,8 +3738,8 @@ static int vmrun_interception(struct vcpu_svm *svm)
        if (nested_svm_check_permissions(svm))
                return 1;
 
-       /* Save rip after vmrun instruction */
-       kvm_rip_write(&svm->vcpu, kvm_rip_read(&svm->vcpu) + 3);
+       if (!kvm_skip_emulated_instruction(&svm->vcpu))
+               return 1;
 
        if (!nested_svm_vmrun(svm))
                return 1;
@@ -3779,7 +3775,6 @@ 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);
 
@@ -3795,7 +3790,6 @@ 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);
@@ -3820,7 +3814,6 @@ 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);
 }
 
@@ -3843,7 +3836,6 @@ 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);
        }
 
@@ -3920,7 +3912,6 @@ 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);
 }
 
@@ -4250,7 +4241,6 @@ 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);
        }
 }
@@ -4456,7 +4446,6 @@ 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