[PATCH 1/3] KVM: x86: Insert "AMD" in KVM_X86_FEATURE_PSFD

[PATCH 1/3] KVM: x86: Insert "AMD" in KVM_X86_FEATURE_PSFD

[Jim Mattson]

Intel and AMD have separate CPUID bits for each SPEC_CTRL bit. In the
case of every bit other than PFSD, the Intel CPUID bit has no vendor
name qualifier, but the AMD CPUID bit does. For consistency, rename
KVM_X86_FEATURE_PSFD to KVM_X86_FEATURE_AMD_PSFD.

No functional change intended.

Signed-off-by: Jim Mattson <jmattson@google.com>
Cc: Babu Moger <Babu.Moger@amd.com>
---
 arch/x86/kvm/cpuid.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 75dcf7a72605..07be45c5bb93 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -62,7 +62,7 @@ u32 xstate_required_size(u64 xstate_bv, bool compacted)
  * This one is tied to SSB in the user API, and not
  * visible in /proc/cpuinfo.
  */
-#define KVM_X86_FEATURE_PSFD		(13*32+28) /* Predictive Store Forwarding Disable */
+#define KVM_X86_FEATURE_AMD_PSFD	(13*32+28) /* Predictive Store Forwarding Disable */
 
 #define F feature_bit
 #define SF(name) (boot_cpu_has(X86_FEATURE_##name) ? F(name) : 0)
@@ -673,7 +673,7 @@ void kvm_set_cpu_caps(void)
 		F(CLZERO) | F(XSAVEERPTR) |
 		F(WBNOINVD) | F(AMD_IBPB) | F(AMD_IBRS) | F(AMD_SSBD) | F(VIRT_SSBD) |
 		F(AMD_SSB_NO) | F(AMD_STIBP) | F(AMD_STIBP_ALWAYS_ON) |
-		__feature_bit(KVM_X86_FEATURE_PSFD)
+		__feature_bit(KVM_X86_FEATURE_AMD_PSFD)
 	);
 
 	/*
-- 
2.37.2.672.g94769d06f0-goog

[PATCH 2/3] KVM: x86: Report CPUID.7.1 support on CPUs with CPUID.7 indices > 1

[Jim Mattson]

Previously, KVM reported support for CPUID.(EAX=7,ECX=1) only if the
maximum leaf 7 index on the host was exactly 1. A recent microcode
patch for Ice Lake raised the maximum leaf 7 index from 0 to 2,
skipping right over 1. Though that patch left CPUID.(EAX=7,ECX=1)
filled with zeros on Ice Lake, it nonetheless exposed this bug.

Report CPUID.(EAX=7,ECX=1) support if the maximum leaf 7 index on the
host is at least 1.

Cc: Sean Christopherson <seanjc@google.com>
Fixes: bcf600ca8d21 ("KVM: x86: Remove the unnecessary loop on CPUID 0x7 sub-leafs")
Signed-off-by: Jim Mattson <jmattson@google.com>
---
 arch/x86/kvm/cpuid.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 07be45c5bb93..64cdabb3cb2c 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -886,7 +886,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		cpuid_entry_override(entry, CPUID_7_EDX);
 
 		/* KVM only supports 0x7.0 and 0x7.1, capped above via min(). */
-		if (entry->eax == 1) {
+		if (entry->eax >= 1) {
 			entry = do_host_cpuid(array, function, 1);
 			if (!entry)
 				goto out;
-- 
2.37.2.672.g94769d06f0-goog

[PATCH 3/3] KVM: x86: Expose Predictive Store Forwarding Disable on Intel parts

[Jim Mattson]

Intel enumerates support for PSFD in CPUID.(EAX=7,ECX=2):EDX.PSFD[bit
0]. Report support for this feature in KVM if it is available on the
host.

Presumably, this feature bit, like its AMD counterpart, is not welcome
in cpufeatures.h, so add a local definition of this feature in KVM.

Signed-off-by: Jim Mattson <jmattson@google.com>
---
 arch/x86/kvm/cpuid.c | 23 +++++++++++++++++------
 1 file changed, 17 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 64cdabb3cb2c..b5af9e451bef 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -62,6 +62,7 @@ u32 xstate_required_size(u64 xstate_bv, bool compacted)
  * This one is tied to SSB in the user API, and not
  * visible in /proc/cpuinfo.
  */
+#define KVM_X86_FEATURE_PSFD		0          /* Predictive Store Forwarding Disable */
 #define KVM_X86_FEATURE_AMD_PSFD	(13*32+28) /* Predictive Store Forwarding Disable */
 
 #define F feature_bit
@@ -677,9 +678,9 @@ void kvm_set_cpu_caps(void)
 	);
 
 	/*
-	 * AMD has separate bits for each SPEC_CTRL bit.
-	 * arch/x86/kernel/cpu/bugs.c is kind enough to
-	 * record that in cpufeatures so use them.
+	 * AMD has separate bits for each SPEC_CTRL bit.  Except for
+	 * PSFD, arch/x86/kernel/cpu/bugs.c is kind enough to record
+	 * that in cpufeatures so use them.
 	 */
 	if (boot_cpu_has(X86_FEATURE_IBPB))
 		kvm_cpu_cap_set(X86_FEATURE_AMD_IBPB);
@@ -880,13 +881,13 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		break;
 	/* function 7 has additional index. */
 	case 7:
-		entry->eax = min(entry->eax, 1u);
+		/* KVM only supports leaf 7 indices 0 through 2. */
+		max_idx = entry->eax = min(entry->eax, 2u);
 		cpuid_entry_override(entry, CPUID_7_0_EBX);
 		cpuid_entry_override(entry, CPUID_7_ECX);
 		cpuid_entry_override(entry, CPUID_7_EDX);
 
-		/* KVM only supports 0x7.0 and 0x7.1, capped above via min(). */
-		if (entry->eax >= 1) {
+		if (max_idx >= 1) {
 			entry = do_host_cpuid(array, function, 1);
 			if (!entry)
 				goto out;
@@ -896,6 +897,16 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 			entry->ecx = 0;
 			entry->edx = 0;
 		}
+		if (max_idx >= 2) {
+			entry = do_host_cpuid(array, function, 2);
+			if (!entry)
+				goto out;
+
+			entry->eax = 0;
+			entry->ebx = 0;
+			entry->ecx = 0;
+			entry->edx &= BIT(KVM_X86_FEATURE_PSFD);
+		}
 		break;
 	case 9:
 		break;
-- 
2.37.2.672.g94769d06f0-goog

Re: [PATCH 2/3] KVM: x86: Report CPUID.7.1 support on CPUs with CPUID.7 indices > 1

[Sean Christopherson]

On Fri, Aug 26, 2022, Jim Mattson wrote:
> Previously, KVM reported support for CPUID.(EAX=7,ECX=1) only if the
> maximum leaf 7 index on the host was exactly 1. A recent microcode
> patch for Ice Lake raised the maximum leaf 7 index from 0 to 2,
> skipping right over 1. Though that patch left CPUID.(EAX=7,ECX=1)
> filled with zeros on Ice Lake, it nonetheless exposed this bug.
> 
> Report CPUID.(EAX=7,ECX=1) support if the maximum leaf 7 index on the
> host is at least 1.
> 
> Cc: Sean Christopherson <seanjc@google.com>
> Fixes: bcf600ca8d21 ("KVM: x86: Remove the unnecessary loop on CPUID 0x7 sub-leafs")
> Signed-off-by: Jim Mattson <jmattson@google.com>
> ---
>  arch/x86/kvm/cpuid.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 07be45c5bb93..64cdabb3cb2c 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -886,7 +886,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  		cpuid_entry_override(entry, CPUID_7_EDX);
>  
>  		/* KVM only supports 0x7.0 and 0x7.1, capped above via min(). */
> -		if (entry->eax == 1) {
> +		if (entry->eax >= 1) {

But as the comment says, above this is:

		entry->eax = min(entry->eax, 1u);

		...

		/* KVM only supports 0x7.0 and 0x7.1, capped above via min(). */
		if (entry->eax == 1) {

What am I missing?

Re: [PATCH 2/3] KVM: x86: Report CPUID.7.1 support on CPUs with CPUID.7 indices > 1

[Jim Mattson]

On Fri, Aug 26, 2022 at 4:54 PM Sean Christopherson <seanjc@google.com> wrote:
>
> On Fri, Aug 26, 2022, Jim Mattson wrote:
> > Previously, KVM reported support for CPUID.(EAX=7,ECX=1) only if the
> > maximum leaf 7 index on the host was exactly 1. A recent microcode
> > patch for Ice Lake raised the maximum leaf 7 index from 0 to 2,
> > skipping right over 1. Though that patch left CPUID.(EAX=7,ECX=1)
> > filled with zeros on Ice Lake, it nonetheless exposed this bug.
> >
> > Report CPUID.(EAX=7,ECX=1) support if the maximum leaf 7 index on the
> > host is at least 1.
> >
> > Cc: Sean Christopherson <seanjc@google.com>
> > Fixes: bcf600ca8d21 ("KVM: x86: Remove the unnecessary loop on CPUID 0x7 sub-leafs")
> > Signed-off-by: Jim Mattson <jmattson@google.com>
> > ---
> >  arch/x86/kvm/cpuid.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > index 07be45c5bb93..64cdabb3cb2c 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -886,7 +886,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
> >               cpuid_entry_override(entry, CPUID_7_EDX);
> >
> >               /* KVM only supports 0x7.0 and 0x7.1, capped above via min(). */
> > -             if (entry->eax == 1) {
> > +             if (entry->eax >= 1) {
>
> But as the comment says, above this is:
>
>                 entry->eax = min(entry->eax, 1u);
>
>                 ...
>
>                 /* KVM only supports 0x7.0 and 0x7.1, capped above via min(). */
>                 if (entry->eax == 1) {
>
> What am I missing?

It's not you; it's me. There's no bug here.