On Fri, Nov 16, 2018 at 03:01:10AM +0200, Jarkko Sakkinen wrote:
> From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
>
> CPUID_12_EAX is an Intel-defined feature bits leaf dedicated for SGX
> that enumerates the SGX instruction sets that are supported by the
> CPU, e.g. SGX1, SGX2, etc... Because Linux currently only cares about
> two bits (SGX1 and SGX2) and there are currently only four documented
> bits in total, relocate the bits to Linux-defined word 8 to conserve
> space.
>
> But, keep the bit positions identical between the Intel-defined value
> and the Linux-defined value, e.g. keep SGX1 at bit 0. This allows KVM
> to use its existing code for probing guest CPUID bits using Linux's
> X86_FEATURE_* definitions. To do so, shift around some existing bits
> to effectively reserve bits 0-7 of word 8 for SGX sub-features.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
> Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
> ---
> arch/x86/include/asm/cpufeatures.h | 21 +++++++++++++++------
> arch/x86/kernel/cpu/scattered.c | 2 ++
> tools/arch/x86/include/asm/cpufeatures.h | 21 +++++++++++++++------
> 3 files changed, 32 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index da7fed4939a3..afdf5f2e13b5 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -222,12 +222,21 @@
> #define X86_FEATURE_L1TF_PTEINV ( 7*32+29) /* "" L1TF workaround PTE inversion */
> #define X86_FEATURE_IBRS_ENHANCED ( 7*32+30) /* Enhanced IBRS */
>
> -/* Virtualization flags: Linux defined, word 8 */
> -#define X86_FEATURE_TPR_SHADOW ( 8*32+ 0) /* Intel TPR Shadow */
> -#define X86_FEATURE_VNMI ( 8*32+ 1) /* Intel Virtual NMI */
> -#define X86_FEATURE_FLEXPRIORITY ( 8*32+ 2) /* Intel FlexPriority */
> -#define X86_FEATURE_EPT ( 8*32+ 3) /* Intel Extended Page Table */
> -#define X86_FEATURE_VPID ( 8*32+ 4) /* Intel Virtual Processor ID */
> +/*
> + * Scattered Intel features: Linux defined, word 8.
> + *
> + * Note that the bit location of the SGX features is meaningful as KVM expects
> + * the Linux defined bit to match the Intel defined bit, e.g. X86_FEATURE_SGX1
> + * must remain at bit 0, SGX2 at bit 1, etc...
> + */
> +#define X86_FEATURE_SGX1 ( 8*32+ 0) /* SGX1 leaf functions */
> +#define X86_FEATURE_SGX2 ( 8*32+ 1) /* SGX2 leaf functions */
> +
Yeah, add here ^^^^
/* Bits [0:7] are reserved for SGX */
or so, so that people don't use those. Once CPUID(12) gets more bits
added to it, I don't see anything wrong with allocating a separate leaf
for that.
BUT(!), the question then is whether kvm would still be ok with that?
I'm thinking yes, as it will simply use the new definitions, or?
--
Regards/Gruss,
Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
