linux-kernel - [RFC PATCH 17/22] x86/fpu/xstate: Extend the table for mapping xstate components with features

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Date:   Thu,  1 Oct 2020 13:39:08 -0700
From:   "Chang S. Bae" <chang.seok.bae@...el.com>
To:     tglx@...utronix.de, mingo@...nel.org, bp@...e.de, luto@...nel.org,
        x86@...nel.org
Cc:     len.brown@...el.com, dave.hansen@...el.com, jing2.liu@...el.com,
        ravi.v.shankar@...el.com, linux-kernel@...r.kernel.org,
        chang.seok.bae@...el.com
Subject: [RFC PATCH 17/22] x86/fpu/xstate: Extend the table for mapping xstate components with features

At compile-time xfeatures_mask_all includes all possible XCR0 features. At
run-time fpu__init_system_xstate() clears features in xfeatures_mask_all
that are not enabled in CPUID. It does this by looping through all possible
XCR0 features.

Update the code to handle the possibility that there will be gaps in the
XCR0 feature bit numbers.

No functional change, until hardware with bit number gaps in XCR0.

Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Reviewed-by: Len Brown <len.brown@...el.com>
Cc: x86@...nel.org
Cc: linux-kernel@...r.kernel.org
---
 arch/x86/kernel/fpu/xstate.c | 39 ++++++++++++++++++++++--------------
 1 file changed, 24 insertions(+), 15 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 13e8eff7a23b..eaada4a38153 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -41,17 +41,22 @@ static const char *xfeature_names[] =
 	"unknown xstate feature"	,
 };
 
-static short xsave_cpuid_features[] __initdata = {
-	X86_FEATURE_FPU,
-	X86_FEATURE_XMM,
-	X86_FEATURE_AVX,
-	X86_FEATURE_MPX,
-	X86_FEATURE_MPX,
-	X86_FEATURE_AVX512F,
-	X86_FEATURE_AVX512F,
-	X86_FEATURE_AVX512F,
-	X86_FEATURE_INTEL_PT,
-	X86_FEATURE_PKU,
+struct xfeature_capflag_info {
+	int xfeature_idx;
+	short cpu_cap;
+};
+
+static struct xfeature_capflag_info xfeature_capflags[] __initdata = {
+	{ XFEATURE_FP,				X86_FEATURE_FPU },
+	{ XFEATURE_SSE,				X86_FEATURE_XMM },
+	{ XFEATURE_YMM,				X86_FEATURE_AVX },
+	{ XFEATURE_BNDREGS,			X86_FEATURE_MPX },
+	{ XFEATURE_BNDCSR,			X86_FEATURE_MPX },
+	{ XFEATURE_OPMASK,			X86_FEATURE_AVX512F },
+	{ XFEATURE_ZMM_Hi256,			X86_FEATURE_AVX512F },
+	{ XFEATURE_Hi16_ZMM,			X86_FEATURE_AVX512F },
+	{ XFEATURE_PT_UNIMPLEMENTED_SO_FAR,	X86_FEATURE_INTEL_PT },
+	{ XFEATURE_PKRU,			X86_FEATURE_PKU },
 };
 
 /*
@@ -950,11 +955,15 @@ void __init fpu__init_system_xstate(void)
 	}
 
 	/*
-	 * Clear XSAVE features that are disabled in the normal CPUID.
+	 * Cross-check XSAVE feature with CPU capability flag. Clear the
+	 * mask bit for disabled features.
 	 */
-	for (i = 0; i < ARRAY_SIZE(xsave_cpuid_features); i++) {
-		if (!boot_cpu_has(xsave_cpuid_features[i]))
-			xfeatures_mask_all &= ~BIT_ULL(i);
+	for (i = 0; i < ARRAY_SIZE(xfeature_capflags); i++) {
+		short cpu_cap = xfeature_capflags[i].cpu_cap;
+		int idx = xfeature_capflags[i].xfeature_idx;
+
+		if (!boot_cpu_has(cpu_cap))
+			xfeatures_mask_all &= ~BIT_ULL(idx);
 	}
 
 	xfeatures_mask_all &= fpu__get_supported_xfeatures_mask();
-- 
2.17.1