+++ /dev/null
-From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
-From: Maxim Levitsky <mlevitsk@redhat.com>
-Date: Wed, 8 Jul 2020 14:57:31 +0300
-Subject: [PATCH] kvm: x86: replace kvm_spec_ctrl_test_value with runtime test
- on the host
-
-To avoid complex and in some cases incorrect logic in
-kvm_spec_ctrl_test_value, just try the guest's given value on the host
-processor instead, and if it doesn't #GP, allow the guest to set it.
-
-One such case is when host CPU supports STIBP mitigation
-but doesn't support IBRS (as is the case with some Zen2 AMD cpus),
-and in this case we were giving guest #GP when it tried to use STIBP
-
-The reason why can can do the host test is that IA32_SPEC_CTRL msr is
-passed to the guest, after the guest sets it to a non zero value
-for the first time (due to performance reasons),
-and as as result of this, it is pointless to emulate #GP condition on
-this first access, in a different way than what the host CPU does.
-
-This is based on a patch from Sean Christopherson, who suggested this idea.
-
-Fixes: 6441fa6178f5 ("KVM: x86: avoid incorrect writes to host MSR_IA32_SPEC_CTRL")
-Cc: stable@vger.kernel.org
-Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
-Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
-Message-Id: <20200708115731.180097-1-mlevitsk@redhat.com>
-Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
-(cherry picked from commit 841c2be09fe4f495fe5224952a419bd8c7e5b455)
-[ Thomas: resolved merge conflict in arch/x86/kvm/x86.h and
- replicated the change to arch/x86/kvm/svm/svm.c to the in 5.4 not
- yet moved out arch/x86/kvm/svm.c ]
-Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
----
- arch/x86/kvm/svm.c | 2 +-
- arch/x86/kvm/vmx/vmx.c | 2 +-
- arch/x86/kvm/x86.c | 38 +++++++++++++++++++++-----------------
- arch/x86/kvm/x86.h | 2 +-
- 4 files changed, 24 insertions(+), 20 deletions(-)
-
-diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
-index 8d386efc2540..372a958bec72 100644
---- a/arch/x86/kvm/svm.c
-+++ b/arch/x86/kvm/svm.c
-@@ -4327,7 +4327,7 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
- !guest_has_spec_ctrl_msr(vcpu))
- return 1;
-
-- if (data & ~kvm_spec_ctrl_valid_bits(vcpu))
-+ if (kvm_spec_ctrl_test_value(data))
- return 1;
-
- svm->spec_ctrl = data;
-diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
-index e7fd2f00edc1..e177848a3631 100644
---- a/arch/x86/kvm/vmx/vmx.c
-+++ b/arch/x86/kvm/vmx/vmx.c
-@@ -1974,7 +1974,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
- !guest_has_spec_ctrl_msr(vcpu))
- return 1;
-
-- if (data & ~kvm_spec_ctrl_valid_bits(vcpu))
-+ if (kvm_spec_ctrl_test_value(data))
- return 1;
-
- vmx->spec_ctrl = data;
-diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
-index f5a827150664..1330fc4dc7c5 100644
---- a/arch/x86/kvm/x86.c
-+++ b/arch/x86/kvm/x86.c
-@@ -10376,28 +10376,32 @@ bool kvm_arch_no_poll(struct kvm_vcpu *vcpu)
- }
- EXPORT_SYMBOL_GPL(kvm_arch_no_poll);
-
--u64 kvm_spec_ctrl_valid_bits(struct kvm_vcpu *vcpu)
-+
-+int kvm_spec_ctrl_test_value(u64 value)
- {
-- uint64_t bits = SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD;
-+ /*
-+ * test that setting IA32_SPEC_CTRL to given value
-+ * is allowed by the host processor
-+ */
-+
-+ u64 saved_value;
-+ unsigned long flags;
-+ int ret = 0;
-
-- /* The STIBP bit doesn't fault even if it's not advertised */
-- if (!guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL) &&
-- !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS))
-- bits &= ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP);
-- if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL) &&
-- !boot_cpu_has(X86_FEATURE_AMD_IBRS))
-- bits &= ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP);
-+ local_irq_save(flags);
-
-- if (!guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL_SSBD) &&
-- !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD))
-- bits &= ~SPEC_CTRL_SSBD;
-- if (!boot_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) &&
-- !boot_cpu_has(X86_FEATURE_AMD_SSBD))
-- bits &= ~SPEC_CTRL_SSBD;
-+ if (rdmsrl_safe(MSR_IA32_SPEC_CTRL, &saved_value))
-+ ret = 1;
-+ else if (wrmsrl_safe(MSR_IA32_SPEC_CTRL, value))
-+ ret = 1;
-+ else
-+ wrmsrl(MSR_IA32_SPEC_CTRL, saved_value);
-
-- return bits;
-+ local_irq_restore(flags);
-+
-+ return ret;
- }
--EXPORT_SYMBOL_GPL(kvm_spec_ctrl_valid_bits);
-+EXPORT_SYMBOL_GPL(kvm_spec_ctrl_test_value);
-
- EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_exit);
- EXPORT_TRACEPOINT_SYMBOL_GPL(kvm_fast_mmio);
-diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
-index 301286d92432..c520d373790a 100644
---- a/arch/x86/kvm/x86.h
-+++ b/arch/x86/kvm/x86.h
-@@ -368,6 +368,6 @@ static inline bool kvm_pat_valid(u64 data)
-
- void kvm_load_guest_xcr0(struct kvm_vcpu *vcpu);
- void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu);
--u64 kvm_spec_ctrl_valid_bits(struct kvm_vcpu *vcpu);
-+int kvm_spec_ctrl_test_value(u64 value);
-
- #endif