linux-kernel - Re: [PATCH v2] x86: fpu: Keep xfd_state always in sync with MSR_IA32

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Date:   Fri, 12 May 2023 14:52:30 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Adamos Ttofari <attofari@...zon.de>
Cc:     attofari@...zon.de, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Kyle Huey <me@...ehuey.com>,
        "Chang S. Bae" <chang.seok.bae@...el.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86: fpu: Keep xfd_state always in sync with
 MSR_IA32_XFD

On Fri, May 12 2023 at 11:38, Adamos Ttofari wrote:
>  	if (cpu_feature_enabled(X86_FEATURE_XFD))
> -		wrmsrl(MSR_IA32_XFD, init_fpstate.xfd);
> +		xfd_set_state(init_fpstate.xfd);

> @@ -914,8 +915,7 @@ void fpu__resume_cpu(void)
>  				     xfeatures_mask_independent());
>  	}
>  
> -	if (fpu_state_size_dynamic())
> -		wrmsrl(MSR_IA32_XFD, current->thread.fpu.fpstate->xfd);
> +	xfd_update_state(current->thread.fpu.fpstate);

How is that supposed to work?

    this_cpu(xfd_state) == current->thread.fpu.fpstate->xfd

So the MSR write won't happen.

Thanks,

        tglx