Messages in this thread | | | Date | Mon, 24 May 2021 21:50:40 +0000 | From | Sean Christopherson <> | Subject | Re: [PATCH RFC 4/7] kvm: x86: Add new ioctls for XSAVE extension |
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On Sun, Feb 07, 2021, Jing Liu wrote: > The static xstate buffer kvm_xsave contains the extended register > states, but it is not enough for dynamic features with large state. > > Introduce a new capability called KVM_CAP_X86_XSAVE_EXTENSION to > detect if hardware has XSAVE extension (XFD). Meanwhile, add two > new ioctl interfaces to get/set the whole xstate using struct > kvm_xsave_extension buffer containing both static and dynamic > xfeatures. Reuse fill_xsave and load_xsave for both cases. > > Signed-off-by: Jing Liu <jing2.liu@linux.intel.com> > --- > arch/x86/include/uapi/asm/kvm.h | 5 +++ > arch/x86/kvm/x86.c | 70 +++++++++++++++++++++++++-------- > include/uapi/linux/kvm.h | 8 ++++ > 3 files changed, 66 insertions(+), 17 deletions(-) > > diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h > index 89e5f3d1bba8..bf785e89a728 100644 > --- a/arch/x86/include/uapi/asm/kvm.h > +++ b/arch/x86/include/uapi/asm/kvm.h > @@ -362,6 +362,11 @@ struct kvm_xsave { > __u32 region[1024]; > }; > > +/* for KVM_CAP_XSAVE_EXTENSION */ > +struct kvm_xsave_extension { > + __u32 region[3072];
Fool me once, shame on you (Intel). Fool me twice, shame on me (KVM).
As amusing as kvm_xsave_really_extended would be, the required size should be discoverable, not hardcoded. Nothing prevents a hardware vendor from inventing a newfangled feature that requires yet more space.
As an alternative to adding a dedicated capability, can we leverage GET_SUPPORTED_CPUID, leaf CPUID.0xD, to enumerate the minimum required size and state that the new ioctl() is available if the min size is greater than 1024? Or is that unnecessarily convoluted...
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