arch/x86/include/asm/nospec-branch.h | 2 +- arch/x86/kernel/cpu/bugs.c | 16 ++++++++++------ arch/x86/kvm/vmx/vmx.c | 2 +- 3 files changed, 12 insertions(+), 8 deletions(-)
The static key mmio_stale_data_clear controls the KVM-only mitigation for
MMIO Stale Data vulnerability. Rename it to reflect its purpose.
No functional change.
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
---
arch/x86/include/asm/nospec-branch.h | 2 +-
arch/x86/kernel/cpu/bugs.c | 16 ++++++++++------
arch/x86/kvm/vmx/vmx.c | 2 +-
3 files changed, 12 insertions(+), 8 deletions(-)
diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 8a5cc8e70439e10aab4eeb5b0f5e116cf635b43d..c0474e2b741737dad129159adf3b5fc056b6097c 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -561,7 +561,7 @@ DECLARE_STATIC_KEY_FALSE(mds_idle_clear);
DECLARE_STATIC_KEY_FALSE(switch_mm_cond_l1d_flush);
-DECLARE_STATIC_KEY_FALSE(mmio_stale_data_clear);
+DECLARE_STATIC_KEY_FALSE(cpu_buf_vm_clear);
extern u16 mds_verw_sel;
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 4386aa6c69e12c9a8d66758e9f7cfff816ccbbe3..dcf029fed3beec38a2e8b6292ec7d0660f3ec678 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -128,9 +128,13 @@ EXPORT_SYMBOL_GPL(mds_idle_clear);
*/
DEFINE_STATIC_KEY_FALSE(switch_mm_cond_l1d_flush);
-/* Controls CPU Fill buffer clear before KVM guest MMIO accesses */
-DEFINE_STATIC_KEY_FALSE(mmio_stale_data_clear);
-EXPORT_SYMBOL_GPL(mmio_stale_data_clear);
+/*
+ * Controls CPU Fill buffer clear before VMenter. This is a subset of
+ * X86_FEATURE_CLEAR_CPU_BUF, and should only be enabled when KVM-only
+ * mitigation is required
+ */
+DEFINE_STATIC_KEY_FALSE(cpu_buf_vm_clear);
+EXPORT_SYMBOL_GPL(cpu_buf_vm_clear);
void __init cpu_select_mitigations(void)
{
@@ -450,9 +454,9 @@ static void __init mmio_select_mitigation(void)
* mitigations, disable KVM-only mitigation in that case.
*/
if (boot_cpu_has(X86_FEATURE_CLEAR_CPU_BUF))
- static_branch_disable(&mmio_stale_data_clear);
+ static_branch_disable(&cpu_buf_vm_clear);
else
- static_branch_enable(&mmio_stale_data_clear);
+ static_branch_enable(&cpu_buf_vm_clear);
/*
* If Processor-MMIO-Stale-Data bug is present and Fill Buffer data can
@@ -572,7 +576,7 @@ static void __init md_clear_update_mitigation(void)
taa_select_mitigation();
}
/*
- * MMIO_MITIGATION_OFF is not checked here so that mmio_stale_data_clear
+ * MMIO_MITIGATION_OFF is not checked here so that cpu_buf_vm_clear
* gets updated correctly as per X86_FEATURE_CLEAR_CPU_BUF state.
*/
if (boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA)) {
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 5c5766467a61d434ba2baa79a5faba99bcbd9997..c79720aad3df265ec8060dfe754bc816104f8c7b 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -7361,7 +7361,7 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu,
*/
if (static_branch_unlikely(&vmx_l1d_should_flush))
vmx_l1d_flush(vcpu);
- else if (static_branch_unlikely(&mmio_stale_data_clear) &&
+ else if (static_branch_unlikely(&cpu_buf_vm_clear) &&
kvm_arch_has_assigned_device(vcpu->kvm))
mds_clear_cpu_buffers();
---
base-commit: 0af2f6be1b4281385b618cb86ad946eded089ac8
change-id: 20250410-mmio-rename-cf8acecb563eOn Thu, Apr 10, 2025, Pawan Gupta wrote: > The static key mmio_stale_data_clear controls the KVM-only mitigation for > MMIO Stale Data vulnerability. Rename it to reflect its purpose. > > No functional change. > > Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com> > --- > arch/x86/include/asm/nospec-branch.h | 2 +- > arch/x86/kernel/cpu/bugs.c | 16 ++++++++++------ > arch/x86/kvm/vmx/vmx.c | 2 +- > 3 files changed, 12 insertions(+), 8 deletions(-) > > diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h > index 8a5cc8e70439e10aab4eeb5b0f5e116cf635b43d..c0474e2b741737dad129159adf3b5fc056b6097c 100644 > --- a/arch/x86/include/asm/nospec-branch.h > +++ b/arch/x86/include/asm/nospec-branch.h > @@ -561,7 +561,7 @@ DECLARE_STATIC_KEY_FALSE(mds_idle_clear); > > DECLARE_STATIC_KEY_FALSE(switch_mm_cond_l1d_flush); > > -DECLARE_STATIC_KEY_FALSE(mmio_stale_data_clear); > +DECLARE_STATIC_KEY_FALSE(cpu_buf_vm_clear); Could we tack on "if_mmio" or something? E.g. cpu_buf_vm_clear_if_mmio. FWIW, I don't love that name, so if anyone can come up with something better... I like the idea of tying the static key back to X86_FEATURE_CLEAR_CPU_BUF, but when looking at just the usage in KVM, "cpu_buf_vm_clear" doesn't provide any hints as to when/why KVM needs to clear buffers.
On Thu, Apr 10, 2025 at 01:39:28PM -0700, Sean Christopherson wrote: > On Thu, Apr 10, 2025, Pawan Gupta wrote: > > The static key mmio_stale_data_clear controls the KVM-only mitigation for > > MMIO Stale Data vulnerability. Rename it to reflect its purpose. > > > > No functional change. > > > > Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com> > > --- > > arch/x86/include/asm/nospec-branch.h | 2 +- > > arch/x86/kernel/cpu/bugs.c | 16 ++++++++++------ > > arch/x86/kvm/vmx/vmx.c | 2 +- > > 3 files changed, 12 insertions(+), 8 deletions(-) > > > > diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h > > index 8a5cc8e70439e10aab4eeb5b0f5e116cf635b43d..c0474e2b741737dad129159adf3b5fc056b6097c 100644 > > --- a/arch/x86/include/asm/nospec-branch.h > > +++ b/arch/x86/include/asm/nospec-branch.h > > @@ -561,7 +561,7 @@ DECLARE_STATIC_KEY_FALSE(mds_idle_clear); > > > > DECLARE_STATIC_KEY_FALSE(switch_mm_cond_l1d_flush); > > > > -DECLARE_STATIC_KEY_FALSE(mmio_stale_data_clear); > > +DECLARE_STATIC_KEY_FALSE(cpu_buf_vm_clear); > > Could we tack on "if_mmio" or something? E.g. cpu_buf_vm_clear_if_mmio. FWIW, > I don't love that name, so if anyone can come up with something better... Keeping it generic has an advantage that it plays nicely with "Attack vector controls" series: https://lore.kernel.org/lkml/20250310164023.779191-1-david.kaplan@amd.com/ The idea being to allow mitigations to be enabled/disabled based on user-defined threat model. MDS/TAA mitigations may be able to take advantage this KVM-only control. > I like the idea of tying the static key back to X86_FEATURE_CLEAR_CPU_BUF, but > when looking at just the usage in KVM, "cpu_buf_vm_clear" doesn't provide any > hints as to when/why KVM needs to clear buffers. Thats fair, can we cover that with a comment like below: --- diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index c79720aad3df..cddad4a6eb46 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -7358,6 +7358,10 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu, * mitigation for MDS is done late in VMentry and is still * executed in spite of L1D Flush. This is because an extra VERW * should not matter much after the big hammer L1D Flush. + * + * cpu_buf_vm_clear is used when system is not vulnerable to MDS/TAA, + * but is affected by MMIO Stale Data that only needs mitigation + * against a rogue guest. */ if (static_branch_unlikely(&vmx_l1d_should_flush)) vmx_l1d_flush(vcpu);
On Thu, Apr 10, 2025, Pawan Gupta wrote: > On Thu, Apr 10, 2025 at 01:39:28PM -0700, Sean Christopherson wrote: > > On Thu, Apr 10, 2025, Pawan Gupta wrote: > > > The static key mmio_stale_data_clear controls the KVM-only mitigation for > > > MMIO Stale Data vulnerability. Rename it to reflect its purpose. > > > > > > No functional change. > > > > > > Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com> > > > --- > > > arch/x86/include/asm/nospec-branch.h | 2 +- > > > arch/x86/kernel/cpu/bugs.c | 16 ++++++++++------ > > > arch/x86/kvm/vmx/vmx.c | 2 +- > > > 3 files changed, 12 insertions(+), 8 deletions(-) > > > > > > diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h > > > index 8a5cc8e70439e10aab4eeb5b0f5e116cf635b43d..c0474e2b741737dad129159adf3b5fc056b6097c 100644 > > > --- a/arch/x86/include/asm/nospec-branch.h > > > +++ b/arch/x86/include/asm/nospec-branch.h > > > @@ -561,7 +561,7 @@ DECLARE_STATIC_KEY_FALSE(mds_idle_clear); > > > > > > DECLARE_STATIC_KEY_FALSE(switch_mm_cond_l1d_flush); > > > > > > -DECLARE_STATIC_KEY_FALSE(mmio_stale_data_clear); > > > +DECLARE_STATIC_KEY_FALSE(cpu_buf_vm_clear); > > > > Could we tack on "if_mmio" or something? E.g. cpu_buf_vm_clear_if_mmio. FWIW, > > I don't love that name, so if anyone can come up with something better... > > Keeping it generic has an advantage that it plays nicely with "Attack vector > controls" series: > > https://lore.kernel.org/lkml/20250310164023.779191-1-david.kaplan@amd.com/ > > The idea being to allow mitigations to be enabled/disabled based on > user-defined threat model. MDS/TAA mitigations may be able to take > advantage this KVM-only control. > > > I like the idea of tying the static key back to X86_FEATURE_CLEAR_CPU_BUF, but > > when looking at just the usage in KVM, "cpu_buf_vm_clear" doesn't provide any > > hints as to when/why KVM needs to clear buffers. > > Thats fair, can we cover that with a comment like below: > > --- > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index c79720aad3df..cddad4a6eb46 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -7358,6 +7358,10 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu, > * mitigation for MDS is done late in VMentry and is still > * executed in spite of L1D Flush. This is because an extra VERW > * should not matter much after the big hammer L1D Flush. > + * > + * cpu_buf_vm_clear is used when system is not vulnerable to MDS/TAA, > + * but is affected by MMIO Stale Data that only needs mitigation > + * against a rogue guest. Would this be accurate? * Clear CPU buffers if the vCPU has access to host MMIO, and the CPU * is NOT vulnerable to MSD/TAA but is affected by MMIO Stale Data, as * indicated by cpu_buf_vm_clear. If the CPU is vulnerable to MDS/TAA, * CPU buffers will be cleared just before every VM-Entry. > */ > if (static_branch_unlikely(&vmx_l1d_should_flush)) > vmx_l1d_flush(vcpu);
On Thu, Apr 10, 2025 at 04:35:58PM -0700, Sean Christopherson wrote: > > > I like the idea of tying the static key back to X86_FEATURE_CLEAR_CPU_BUF, but > > > when looking at just the usage in KVM, "cpu_buf_vm_clear" doesn't provide any > > > hints as to when/why KVM needs to clear buffers. > > > > Thats fair, can we cover that with a comment like below: > > > > --- > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > > index c79720aad3df..cddad4a6eb46 100644 > > --- a/arch/x86/kvm/vmx/vmx.c > > +++ b/arch/x86/kvm/vmx/vmx.c > > @@ -7358,6 +7358,10 @@ static noinstr void vmx_vcpu_enter_exit(struct kvm_vcpu *vcpu, > > * mitigation for MDS is done late in VMentry and is still > > * executed in spite of L1D Flush. This is because an extra VERW > > * should not matter much after the big hammer L1D Flush. > > + * > > + * cpu_buf_vm_clear is used when system is not vulnerable to MDS/TAA, > > + * but is affected by MMIO Stale Data that only needs mitigation > > + * against a rogue guest. > > Would this be accurate? I believe this is accurate as things stand today. But, when Attack Vector Control series leverages cpu_buf_vm_clear, the comment also needs to be updated.
On Thu, Apr 10, 2025 at 10:49:51AM -0700, Pawan Gupta wrote:
> The static key mmio_stale_data_clear controls the KVM-only mitigation for
> MMIO Stale Data vulnerability. Rename it to reflect its purpose.
>
> No functional change.
>
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
> ---
> arch/x86/include/asm/nospec-branch.h | 2 +-
> arch/x86/kernel/cpu/bugs.c | 16 ++++++++++------
> arch/x86/kvm/vmx/vmx.c | 2 +-
> 3 files changed, 12 insertions(+), 8 deletions(-)
Acked-by: Borislav Petkov (AMD) <bp@alien8.de>
--
Regards/Gruss,
Boris.
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