File xsa435-1.patch of Package xen.31431

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File xsa435-1.patch of Package xen.31431

From e3e3edb0420f7a42fda28187eb6fe362126c2e30 Mon Sep 17 00:00:00 2001
From: Andrew Cooper <andrew.cooper3@citrix.com>
Date: Mon, 27 Feb 2023 15:36:49 +0000
Subject: x86/cpu-policy: Hide CLWB by default on SKX/CLX/CPX

The August 2023 microcode for GDS has an impact on the CLWB instruction.  See
code comments for full details.

This is part of XSA-435 / CVE-2022-40982

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/cpu/intel.c
+++ b/xen/arch/x86/cpu/intel.c
@@ -448,6 +448,18 @@ static void init_intel(struct cpuinfo_x8
 	     ( c->cpuid_level >= 0x00000006 ) &&
 	     ( cpuid_eax(0x00000006) & (1u<<2) ) )
 		__set_bit(X86_FEATURE_ARAT, c->x86_capability);
+
+	/*
+	 * The Gather Data Sampling microcode mitigation (August 2023) has an
+	 * adverse performance impact on the CLWB instruction on SKX/CLX/CPX.
+	 *
+	 * On this model, CLWB has equivalent behaviour to CLFLUSHOPT but the
+	 * latter is not impacted.  Hide CLWB to cause Xen to fall back to
+	 * using CLFLUSHOPT instead.
+	 */
+	if (c == &boot_cpu_data &&
+	    c->x86 == 6 && c->x86_model == 0x55 /* INTEL_FAM6_SKYLAKE_X */)
+		setup_clear_cpu_cap(X86_FEATURE_CLWB);
 }
 
 static const struct cpu_dev intel_cpu_dev = {
--- a/xen/include/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -214,7 +214,7 @@ XEN_CPUFEATURE(ADX,           5*32+19) /
 XEN_CPUFEATURE(SMAP,          5*32+20) /*S  Supervisor Mode Access Prevention */
 XEN_CPUFEATURE(AVX512IFMA,    5*32+21) /*A  AVX-512 Integer Fused Multiply Add */
 XEN_CPUFEATURE(CLFLUSHOPT,    5*32+23) /*A  CLFLUSHOPT instruction */
-XEN_CPUFEATURE(CLWB,          5*32+24) /*A  CLWB instruction */
+XEN_CPUFEATURE(CLWB,          5*32+24) /*!A CLWB instruction */
 XEN_CPUFEATURE(AVX512PF,      5*32+26) /*A  AVX-512 Prefetch Instructions */
 XEN_CPUFEATURE(AVX512ER,      5*32+27) /*A  AVX-512 Exponent & Reciprocal Instrs */
 XEN_CPUFEATURE(AVX512CD,      5*32+28) /*A  AVX-512 Conflict Detection Instrs */

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File xsa435-1.patch of Package xen.31431

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