Commit 0fe4ff88 authored by Noah Goldstein's avatar Noah Goldstein Committed by Borislav Petkov
Browse files

x86/fpu: Correct AVX512 state tracking 



Add a separate, local mask for tracking AVX512 usage which does not
include the opmask xfeature set. Opmask registers usage does not cause
frequency throttling so it is a completely unnecessary false positive.

While at it, carve it out into a separate function to keep that
abomination extracted out.

 [ bp: Rediff and cleanup ontop of 5.16-rc1. ]

Signed-off-by: default avatarNoah Goldstein <goldstein.w.n@gmail.com>
Signed-off-by: default avatarBorislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20210920053951.4093668-1-goldstein.w.n@gmail.com
parent fa55b7dc

arch/x86/kernel/fpu/core.c

+14 −7
Original line number Diff line number Diff line
@@ -98,6 +98,19 @@ bool irq_fpu_usable(void) 
}

EXPORT_SYMBOL(irq_fpu_usable);



/*

 * Track AVX512 state use because it is known to slow the max clock

 * speed of the core.

 */

static void update_avx_timestamp(struct fpu *fpu)

{



#define AVX512_TRACKING_MASK	(XFEATURE_MASK_ZMM_Hi256 | XFEATURE_MASK_Hi16_ZMM)



	if (fpu->fpstate->regs.xsave.header.xfeatures & AVX512_TRACKING_MASK)

		fpu->avx512_timestamp = jiffies;

}



/*

 * Save the FPU register state in fpu->fpstate->regs. The register state is

 * preserved.
@@ -116,13 +129,7 @@ void save_fpregs_to_fpstate(struct fpu *fpu) 
{

	if (likely(use_xsave())) {

		os_xsave(fpu->fpstate);



		/*

		 * AVX512 state is tracked here because its use is

		 * known to slow the max clock speed of the core.

		 */

		if (fpu->fpstate->regs.xsave.header.xfeatures & XFEATURE_MASK_AVX512)

			fpu->avx512_timestamp = jiffies;

		update_avx_timestamp(fpu);

		return;

	}