[08/61] KVM: x86: Warn on zero-size save state for valid CPUID 0xD.N sub-leaf
diff mbox series

Message ID 20200201185218.24473-9-sean.j.christopherson@intel.com
State New
Headers show
Series
  • KVM: x86: Introduce KVM cpu caps
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Commit Message

Sean Christopherson Feb. 1, 2020, 6:51 p.m. UTC
WARN if the save state size for a valid XCR0-managed sub-leaf is zero,
which would indicate a KVM or CPU bug.  Add a comment to explain why KVM
WARNs so the reader doesn't have to tease out the relevant bits from
Intel's SDM and KVM's XCR0/XSS code.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/kvm/cpuid.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

Comments

Vitaly Kuznetsov Feb. 7, 2020, 3:54 p.m. UTC | #1
Sean Christopherson <sean.j.christopherson@intel.com> writes:

> WARN if the save state size for a valid XCR0-managed sub-leaf is zero,
> which would indicate a KVM or CPU bug.  Add a comment to explain why KVM
> WARNs so the reader doesn't have to tease out the relevant bits from
> Intel's SDM and KVM's XCR0/XSS code.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
>  arch/x86/kvm/cpuid.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index fd9b29aa7abc..424dde41cb5d 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -677,10 +677,17 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
>  				goto out;
>  
>  			do_host_cpuid(&entry[i], function, idx);
> -			if (entry[i].eax == 0)
> -				continue;
> -			if (WARN_ON_ONCE(entry[i].ecx & 1))
> +
> +			/*
> +			 * The @supported check above should have filtered out
> +			 * invalid sub-leafs as well as sub-leafs managed by

Is it 'sub-leafs' or 'sub-leaves' actually? :-)

> +			 * IA32_XSS MSR.  Only XCR0-managed sub-leafs should
> +			 * reach this point, and they should have a non-zero
> +			 * save state size.
> +			 */
> +			if (WARN_ON_ONCE(!entry[i].eax || (entry[i].ecx & 1)))
>  				continue;
> +
>  			entry[i].ecx = 0;
>  			entry[i].edx = 0;
>  			++*nent;

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Sean Christopherson Feb. 7, 2020, 3:56 p.m. UTC | #2
On Fri, Feb 07, 2020 at 04:54:59PM +0100, Vitaly Kuznetsov wrote:
> Sean Christopherson <sean.j.christopherson@intel.com> writes:
> 
> > WARN if the save state size for a valid XCR0-managed sub-leaf is zero,
> > which would indicate a KVM or CPU bug.  Add a comment to explain why KVM
> > WARNs so the reader doesn't have to tease out the relevant bits from
> > Intel's SDM and KVM's XCR0/XSS code.
> >
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > ---
> >  arch/x86/kvm/cpuid.c | 13 ++++++++++---
> >  1 file changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > index fd9b29aa7abc..424dde41cb5d 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -677,10 +677,17 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
> >  				goto out;
> >  
> >  			do_host_cpuid(&entry[i], function, idx);
> > -			if (entry[i].eax == 0)
> > -				continue;
> > -			if (WARN_ON_ONCE(entry[i].ecx & 1))
> > +
> > +			/*
> > +			 * The @supported check above should have filtered out
> > +			 * invalid sub-leafs as well as sub-leafs managed by
> 
> Is it 'sub-leafs' or 'sub-leaves' actually? :-)

Yes.  :-D

Patch
diff mbox series

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index fd9b29aa7abc..424dde41cb5d 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -677,10 +677,17 @@  static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
 				goto out;
 
 			do_host_cpuid(&entry[i], function, idx);
-			if (entry[i].eax == 0)
-				continue;
-			if (WARN_ON_ONCE(entry[i].ecx & 1))
+
+			/*
+			 * The @supported check above should have filtered out
+			 * invalid sub-leafs as well as sub-leafs managed by
+			 * IA32_XSS MSR.  Only XCR0-managed sub-leafs should
+			 * reach this point, and they should have a non-zero
+			 * save state size.
+			 */
+			if (WARN_ON_ONCE(!entry[i].eax || (entry[i].ecx & 1)))
 				continue;
+
 			entry[i].ecx = 0;
 			entry[i].edx = 0;
 			++*nent;