linux-kernel - Re: [PATCH v2 1/2] x86/fpu: Extend kernel_fpu_begin

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Date: Thu, 9 May 2024 11:41:23 -0700
From: "Chang S. Bae" <chang.seok.bae@...el.com>
To: Dave Hansen <dave.hansen@...el.com>, <linux-kernel@...r.kernel.org>
CC: <x86@...nel.org>, <platform-driver-x86@...r.kernel.org>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <hdegoede@...hat.com>,
	<ilpo.jarvinen@...ux.intel.com>, <tony.luck@...el.com>,
	<ashok.raj@...el.com>, <jithu.joseph@...el.com>
Subject: Re: [PATCH v2 1/2] x86/fpu: Extend kernel_fpu_begin_mask() to
 initialize AMX state

On 5/9/2024 10:36 AM, Dave Hansen wrote:
> 
> I'd probably just do this:
> 
> +	kernel_fpu_begin();
> +	// AMX *MUST* be in the init state for the wrmsr() to work.
> +	// But, the more in the init state, the less state the test
> +	// has to save and restore.  Just zap everything.
> +	restore_fpregs_from_fpstate(&init_fpstate,	
> +				    fpu_user_cfg.max_features);
> +

I assume that this snippet goes to the IFS driver side. Then, we need to 
introduce and export a new wrapper for this. 
restore_fpregs_from_fpstate() and its arguments are not accessible as of 
now.

Also, I think we should encapsulate them. If we follow this style, we 
could have invoked tilerelease() directly from the idle driver, right?

>          wrmsrl(MSR_ACTIVATE_SCAN, params->activate->data);
>          rdmsrl(MSR_SCAN_STATUS, status.data);
> 
> +	kernel_fpu_end();