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Date: Tue, 2 Nov 2021 17:15:31 +0800
From: Hou Wenlong <houwenlong93@...ux.alibaba.com>
To: kvm@...r.kernel.org
Cc: Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
linux-kernel@...r.kernel.org
Subject: [PATCH v2 3/4] KVM: x86: Use different callback if msr access comes from the emulator
If msr access triggers an exit to userspace, the
complete_userspace_io callback would skip instruction by vendor
callback for kvm_skip_emulated_instruction(). However, when msr
access comes from the emulator, e.g. if kvm.force_emulation_prefix
is enabled and the guest uses rdmsr/wrmsr with kvm prefix,
VM_EXIT_INSTRUCTION_LEN in vmcs is invalid and
kvm_emulate_instruction() should be used to skip instruction
instead.
As Sean noted, unlike the previous case, there's no #UD if
unrestricted guest is disabled and the guest accesses an MSR in
Big RM. So the correct way to fix this is to attach a different
callback when the msr access comes from the emulator.
Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Hou Wenlong <houwenlong93@...ux.alibaba.com>
---
arch/x86/kvm/x86.c | 85 +++++++++++++++++++++++++++-------------------
1 file changed, 50 insertions(+), 35 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a961b49c8c44..5eadf5ddba3e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -116,6 +116,7 @@ static void enter_smm(struct kvm_vcpu *vcpu);
static void __kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags);
static void store_regs(struct kvm_vcpu *vcpu);
static int sync_regs(struct kvm_vcpu *vcpu);
+static int kvm_vcpu_do_singlestep(struct kvm_vcpu *vcpu);
static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2);
static void __get_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2);
@@ -1814,18 +1815,45 @@ int kvm_set_msr(struct kvm_vcpu *vcpu, u32 index, u64 data)
}
EXPORT_SYMBOL_GPL(kvm_set_msr);
-static int complete_emulated_rdmsr(struct kvm_vcpu *vcpu)
+static void __complete_emulated_rdmsr(struct kvm_vcpu *vcpu)
{
- int err = vcpu->run->msr.error;
- if (!err) {
+ if (!vcpu->run->msr.error) {
kvm_rax_write(vcpu, (u32)vcpu->run->msr.data);
kvm_rdx_write(vcpu, vcpu->run->msr.data >> 32);
}
+}
+
+static int complete_emulated_msr_access(struct kvm_vcpu *vcpu)
+{
+ if (vcpu->run->msr.error) {
+ kvm_inject_gp(vcpu, 0);
+ return 1;
+ }
+
+ return kvm_emulate_instruction(vcpu, EMULTYPE_NO_DECODE | EMULTYPE_SKIP |
+ EMULTYPE_COMPLETE_USER_EXIT);
+}
+
+static int complete_emulated_rdmsr(struct kvm_vcpu *vcpu)
+{
+ __complete_emulated_rdmsr(vcpu);
- return static_call(kvm_x86_complete_emulated_msr)(vcpu, err);
+ return complete_emulated_msr_access(vcpu);
}
static int complete_emulated_wrmsr(struct kvm_vcpu *vcpu)
+{
+ return complete_emulated_msr_access(vcpu);
+}
+
+static int complete_fast_rdmsr(struct kvm_vcpu *vcpu)
+{
+ __complete_emulated_rdmsr(vcpu);
+
+ return static_call(kvm_x86_complete_emulated_msr)(vcpu, vcpu->run->msr.error);
+}
+
+static int complete_fast_wrmsr(struct kvm_vcpu *vcpu)
{
return static_call(kvm_x86_complete_emulated_msr)(vcpu, vcpu->run->msr.error);
}
@@ -1864,18 +1892,6 @@ static int kvm_msr_user_space(struct kvm_vcpu *vcpu, u32 index,
return 1;
}
-static int kvm_get_msr_user_space(struct kvm_vcpu *vcpu, u32 index, int r)
-{
- return kvm_msr_user_space(vcpu, index, KVM_EXIT_X86_RDMSR, 0,
- complete_emulated_rdmsr, r);
-}
-
-static int kvm_set_msr_user_space(struct kvm_vcpu *vcpu, u32 index, u64 data, int r)
-{
- return kvm_msr_user_space(vcpu, index, KVM_EXIT_X86_WRMSR, data,
- complete_emulated_wrmsr, r);
-}
-
int kvm_emulate_rdmsr(struct kvm_vcpu *vcpu)
{
u32 ecx = kvm_rcx_read(vcpu);
@@ -1884,18 +1900,16 @@ int kvm_emulate_rdmsr(struct kvm_vcpu *vcpu)
r = kvm_get_msr(vcpu, ecx, &data);
- /* MSR read failed? See if we should ask user space */
- if (r && kvm_get_msr_user_space(vcpu, ecx, r)) {
- /* Bounce to user space */
- return 0;
- }
-
if (!r) {
trace_kvm_msr_read(ecx, data);
kvm_rax_write(vcpu, data & -1u);
kvm_rdx_write(vcpu, (data >> 32) & -1u);
} else {
+ /* MSR read failed? See if we should ask user space */
+ if (kvm_msr_user_space(vcpu, ecx, KVM_EXIT_X86_RDMSR, 0,
+ complete_fast_rdmsr, r))
+ return 0;
trace_kvm_msr_read_ex(ecx);
}
@@ -1911,19 +1925,18 @@ int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu)
r = kvm_set_msr(vcpu, ecx, data);
- /* MSR write failed? See if we should ask user space */
- if (r && kvm_set_msr_user_space(vcpu, ecx, data, r))
- /* Bounce to user space */
- return 0;
-
- /* Signal all other negative errors to userspace */
- if (r < 0)
- return r;
-
- if (!r)
+ if (!r) {
trace_kvm_msr_write(ecx, data);
- else
+ } else {
+ /* MSR write failed? See if we should ask user space */
+ if (kvm_msr_user_space(vcpu, ecx, KVM_EXIT_X86_WRMSR, data,
+ complete_fast_wrmsr, r))
+ return 0;
+ /* Signal all other negative errors to userspace */
+ if (r < 0)
+ return r;
trace_kvm_msr_write_ex(ecx, data);
+ }
return static_call(kvm_x86_complete_emulated_msr)(vcpu, r);
}
@@ -7387,7 +7400,8 @@ static int emulator_get_msr(struct x86_emulate_ctxt *ctxt,
r = kvm_get_msr(vcpu, msr_index, pdata);
- if (r && kvm_get_msr_user_space(vcpu, msr_index, r)) {
+ if (r && kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_RDMSR, 0,
+ complete_emulated_rdmsr, r)) {
/* Bounce to user space */
return X86EMUL_IO_NEEDED;
}
@@ -7403,7 +7417,8 @@ static int emulator_set_msr(struct x86_emulate_ctxt *ctxt,
r = kvm_set_msr(vcpu, msr_index, data);
- if (r && kvm_set_msr_user_space(vcpu, msr_index, data, r)) {
+ if (r && kvm_msr_user_space(vcpu, msr_index, KVM_EXIT_X86_WRMSR, data,
+ complete_emulated_wrmsr, r)) {
/* Bounce to user space */
return X86EMUL_IO_NEEDED;
}
--
2.31.1
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