Re: [patch 14/31] x86/fpu: Replace KVMs homebrewn FPU copy from user

Thomas Gleixner
2021-10-13T15:16:11Z

On Wed, Oct 13 2021 at 14:57, Sean Christopherson wrote:
> On Tue, Oct 12, 2021, Borislav Petkov wrote:
>> On Tue, Oct 12, 2021 at 02:00:19AM +0200, Thomas Gleixner wrote:
>> > --- a/arch/x86/include/asm/fpu/api.h
>> > +++ b/arch/x86/include/asm/fpu/api.h
>> > @@ -116,4 +116,7 @@ extern void fpu_init_fpstate_user(struct
>> > /* KVM specific functions */
>> > extern void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask);
>> >
>> > +struct kvm_vcpu;
>> > +extern int fpu_copy_kvm_uabi_to_vcpu(struct fpu *fpu, const void *buf, u64 xcr0, u32 *pkru);
>> > +
>> > #endif /* _ASM_X86_FPU_API_H */
>> > --- a/arch/x86/kernel/fpu/core.c
>> > +++ b/arch/x86/kernel/fpu/core.c
>> > @@ -174,7 +174,43 @@ void fpu_swap_kvm_fpu(struct fpu *save,
>> > fpregs_unlock();
>> > }
>> > EXPORT_SYMBOL_GPL(fpu_swap_kvm_fpu);
>> > -#endif
>> > +
>> > +int fpu_copy_kvm_uabi_to_vcpu(struct fpu *fpu, const void *buf, u64 xcr0,
>> > + u32 *vpkru)
>>
>> Right, except that there's no @vcpu in the args of that function. I
>> guess you could call it
>>
>> fpu_copy_kvm_uabi_to_buf()
>>
>> and that @buf can be
>>
>> vcpu->arch.guest_fpu
>
> But the existing @buf is the userspace pointer, which semantically makes sense
> because the userspace pointer is the "buffer" and the destination @fpu (and @prku)
> is vCPU state, not a buffer.
>
> That said, I also struggled with the lack of @vcpu. What about prepending vcpu_
> to fpu and to pkru? E.g.
>
> int fpu_copy_kvm_uabi_to_vcpu(struct fpu *vcpu_fpu, const void *buf, u64 xcr0,
> u32 *vcpu_pkru)

I've renamed them to:

fpu_copy_kvm_uabi_to_fpstate()
fpu_copy_fpstate_to_kvm_uabi()

See
https://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git/log/?h=x86/fpu-1

Thanks,

tglx