Re: [RFC PATCH v3 01/27] x86/cpufeatures: Add SGX1 and SGX2 sub-features

Jarkko Sakkinen
2021-02-02T17:20:53Z

On Mon, Feb 01, 2021 at 01:01:51PM +1300, Kai Huang wrote:
> On Sat, 30 Jan 2021 15:20:54 +0200 Jarkko Sakkinen wrote:
> > On Wed, Jan 27, 2021 at 12:18:32PM +1300, Kai Huang wrote:
> > > On Tue, 2021-01-26 at 07:34 -0800, Dave Hansen wrote:
> > > > On 1/26/21 1:30 AM, Kai Huang wrote:
> > > > > From: Sean Christopherson <seanjc@google.com>
> > > > >
> > > > > Add SGX1 and SGX2 feature flags, via CPUID.0x12.0x0.EAX, as scattered
> > > > > features, since adding a new leaf for only two bits would be wasteful.
> > > > > As part of virtualizing SGX, KVM will expose the SGX CPUID leafs to its
> > > > > guest, and to do so correctly needs to query hardware and kernel support
> > > > > for SGX1 and SGX2.
> > > >
> > > > It's also not _just_ exposing the CPUID leaves. There are some checks
> > > > here when KVM is emulating some SGX instructions too, right?
> > >
> > > I would say trapping instead of emulating, but yes KVM will do more. However those
> > > are quite details, and I don't think we should put lots of details here. Or perhaps
> > > we can use 'for instance' as brief description:
> > >
> > > As part of virtualizing SGX, KVM will need to use the two flags, for instance, to
> > > expose them to guest.
> > >
> > > ?
> > >
> > > >
> > > > > diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> > > > > index 84b887825f12..18b2d0c8bbbe 100644
> > > > > --- a/arch/x86/include/asm/cpufeatures.h
> > > > > +++ b/arch/x86/include/asm/cpufeatures.h
> > > > > @@ -292,6 +292,8 @@
> > > > >  #define X86_FEATURE_FENCE_SWAPGS_KERNEL (11*32+ 5) /* "" LFENCE in kernel entry SWAPGS path */
> > > > >  #define X86_FEATURE_SPLIT_LOCK_DETECT (11*32+ 6) /* #AC for split lock */
> > > > >  #define X86_FEATURE_PER_THREAD_MBA (11*32+ 7) /* "" Per-thread Memory Bandwidth Allocation */
> > > > > +#define X86_FEATURE_SGX1 (11*32+ 8) /* Software Guard Extensions sub-feature SGX1 */
> > > > > +#define X86_FEATURE_SGX2 (11*32+ 9) /* Software Guard Extensions sub-feature SGX2 */
> > > >
> > > > FWIW, I'm not sure how valuable it is to spell the SGX acronym out three
> > > > times. Can't we use those bytes to put something more useful in that
> > > > comment?
> > >
> > > I think we can remove comment for SGX1, since it is basically SGX.
> > >
> > > For SGX2, how about below?
> > >
> > > /* SGX Enclave Dynamic Memory Management */
> >
> > (EDMM)
>
> Does EDMM obvious to everyone, instead of explicitly saying Enclave Dynamic
> Memory Management?
>
> Also do you think we need a comment for SGX1 bit? I can add /* Basic SGX */,
> but I am not sure whether it is required.

I would put write the whole thing down and put EDMM to parentheses.

For SGX1 I would put "Basic SGX features for enclave construction".

/Jarkko