From: Paolo Bonzini pbonzini@redhat.com Sent: Wednesday, January 5, 2022 9:07 PM
On 1/5/22 13:35, Yang Zhong wrote:
+int fpu_enable_guest_xfd_features(struct fpu_guest *guest_fpu, u64
xfeatures)
+{
- lockdep_assert_preemption_enabled();
The old fpu_update_guest_perm_features(guest_fpu) is equivalent to
fpu_enable_guest_xfd_features(guest_fpu, guest_fpu->perm);
Missing doc comment:
/*
- fpu_enable_guest_xfd_features - Enable xfeatures according to guest
perm
- @guest_fpu: Pointer to the guest FPU container
- @xfeatures: Features requested by guest CPUID
- Enable all dynamic xfeatures according to guest perm and requested
CPUID.
- Invoked if the caller wants to conservatively expand fpstate buffer instead
- of waiting until XCR0 or XFD MSR is written.
- Return: 0 on success, error code otherwise
*/
It's not equivalent. The old interface enables all xfeatures allowed by guest perm while the new one just enables feature bits according to the caller request. It also becomes a more general interface instead of being only for conservative expansion. Since both points in the old comment don't hold now and this function is obvious, we didn't put a comment here (on par with other KVM helpers in that block).
If still necessary we could add one like below:
/* * fpu_enable_guest_xfd_features - Enable xfeatures for guest fpu container * @guest_fpu: Pointer to the guest FPU container * @xfeatures: Features requested by the caller * * Enable dynamic xfeatures and expand guest fpstate buffer accordingly. * KVM should call this function before the requested xfeatures are used * by the guest. * * Return: 0 on success, error code otherwise */
Also, the check for 32-bit is slightly imprecise:
/* Dynamic xfeatures are not supported with 32-bit kernels. */ if (!IS_ENABLED(CONFIG_X86_64))
return 0;
return -EINVAL;since we only get here with xfeatures != 0 (if it compiles, just removing the IS_ENABLED check altogether would be even better). With these changes,
Reviewed-by: Paolo Bonzini pbonzini@redhat.com
Thanks,
Paolo