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

Sean Christopherson
2021-10-13T14:58:33Z

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)