On Wed, Jan 05, 2022 at 02:06:40PM +0100, Paolo Bonzini wrote:
> 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
> */
>
> 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,
>
Paolo, I did 32 bit kernel build tests
(1). w/ IS_ENABLED(CONFIG_X86_64)
if (!IS_ENABLED(CONFIG_X86_64))
return -EINVAL;
This 32 bit kernel can successfully build.
(2). remove IS_ENABLED(CONFIG_X86_64)
The 32 bit kernel build is failed, and the error as:
ld: arch/x86/kernel/fpu/core.o: in function `fpu_enable_guest_xfd_features':
/root/amx/v5/kvm/arch/x86/kernel/fpu/core.c:278: undefined reference to `__xfd_enable_feature'
Seems we need define 32 bit API for __xfd_enable_feature().
I also tried (1) in desktop, but I could not reboot the machine after installed 32 bit kernel.
thanks a lot!
Yang
> Reviewed-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>
> Thanks,
>
> Paolo
