[tip: x86/fpu] x86/fpu: Correct AVX512 state tracking

[tip-bot2 for Noah Goldstein]

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     0fe4ff885f8a50082d9dc241b657472894caba16
Gitweb:        https://git.kernel.org/tip/0fe4ff885f8a50082d9dc241b657472894caba16
Author:        Noah Goldstein <goldstein.w.n@xxxxxxxxx>
AuthorDate:    Tue, 16 Nov 2021 17:14:21 +01:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Tue, 16 Nov 2021 17:19:41 +01:00

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: Noah Goldstein <goldstein.w.n@xxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lore.kernel.org/r/20210920053951.4093668-1-goldstein.w.n@xxxxxxxxx
---
 arch/x86/kernel/fpu/core.c | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 8ea306b..dd3777a 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -99,6 +99,19 @@ 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;
 	}