Re: [Xen-devel] [PATCH 5/6] x86/AMD: Fix handling of FPU pointer on Zen hardware

[Pu Wen <puwen@xxxxxxxx>]

On 2018/12/28 20:40, Andrew Cooper wrote:
> AMD hardware before Zen doesn't safe/restore the FPU error pointers
> unless an unmasked FPU exception is pending.  Zen processors have a
> feature bit indicating that this (mis)behaviour no longer exists.
> 
> Express the common logic in terms of cpu_bug_fpu_err_ptr as Hygon
> processors (being Zen derivatives) won't inherit this behaviour.
...
> diff --git a/xen/arch/x86/xstate.c b/xen/arch/x86/xstate.c
> index 15edd5d..7ca5684 100644
> --- a/xen/arch/x86/xstate.c
> +++ b/xen/arch/x86/xstate.c
> @@ -369,15 +369,13 @@ void xrstor(struct vcpu *v, uint64_t mask)
>       unsigned int faults, prev_faults;
>   
>       /*
> -     * AMD CPUs don't save/restore FDP/FIP/FOP unless an exception
> +     * Some CPUs don't save/restore FDP/FIP/FOP unless an exception
>        * is pending. Clear the x87 state here by setting it to fixed
>        * values. The hypervisor data segment can be sometimes 0 and
>        * sometimes new user value. Both should be ok. Use the FPU saved
>        * data block as a safe address because it should be in L1.
>        */
> -    if ( (mask & ptr->xsave_hdr.xstate_bv & X86_XCR0_FP) &&
> -         !(ptr->fpu_sse.fsw & ~ptr->fpu_sse.fcw & 0x003f) &&
> -         boot_cpu_data.x86_vendor == X86_VENDOR_AMD )
> +    if ( cpu_bug_fpu_err_ptr )
>           asm volatile ( "fnclex\n\t"        /* clear exceptions */
>                          "ffree %%st(7)\n\t" /* clear stack tag */
>                          "fildl %0"          /* load to clear state */

It seems that the functions fpu_fxrstor and fpu_fxsave have the same
problem, even though they are not called on Hygon Dhyana platform.
Should them be fixed in the same way?

-- 
Regards,
Pu Wen

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