linux-kernel - [PATCH v2 07/11] x86/xen: use capabilities instead of fake cpuid values for mwait

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Date:   Thu, 13 Apr 2017 12:11:12 +0200
From:   Juergen Gross <jgross@...e.com>
To:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org
Cc:     boris.ostrovsky@...cle.com, Juergen Gross <jgross@...e.com>
Subject: [PATCH v2 07/11] x86/xen: use capabilities instead of fake cpuid values for mwait

When running as pv domain xen_cpuid() is being used instead of
native_cpuid(). In xen_cpuid() the mwait feature is indicated to be
present or not by special casing the related cpuid leaf.

Instead of delivering fake cpuid values use the cpu capability bit
for mwait instead.

Signed-off-by: Juergen Gross <jgross@...e.com>
---
 arch/x86/xen/enlighten_pv.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 3196961862bc..d43382284ada 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -167,7 +167,6 @@ xen_running_on_version_or_later(unsigned int major, unsigned int minor)
 
 static __read_mostly unsigned int cpuid_leaf1_ecx_mask = ~0;
 
-static __read_mostly unsigned int cpuid_leaf1_ecx_set_mask;
 static __read_mostly unsigned int cpuid_leaf5_ecx_val;
 static __read_mostly unsigned int cpuid_leaf5_edx_val;
 
@@ -176,7 +175,6 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
 {
 	unsigned maskebx = ~0;
 	unsigned maskecx = ~0;
-	unsigned setecx = 0;
 	/*
 	 * Mask out inconvenient features, to try and disable as many
 	 * unsupported kernel subsystems as possible.
@@ -184,7 +182,6 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
 	switch (*ax) {
 	case 1:
 		maskecx = cpuid_leaf1_ecx_mask;
-		setecx = cpuid_leaf1_ecx_set_mask;
 		break;
 
 	case CPUID_MWAIT_LEAF:
@@ -210,7 +207,6 @@ static void xen_cpuid(unsigned int *ax, unsigned int *bx,
 
 	*bx &= maskebx;
 	*cx &= maskecx;
-	*cx |= setecx;
 }
 STACK_FRAME_NON_STANDARD(xen_cpuid); /* XEN_EMULATE_PREFIX */
 
@@ -303,8 +299,6 @@ static void __init xen_init_cpuid_mask(void)
 	/* Xen will set CR4.OSXSAVE if supported and not disabled by force */
 	if ((cx & xsave_mask) != xsave_mask)
 		cpuid_leaf1_ecx_mask &= ~xsave_mask; /* disable XSAVE & OSXSAVE */
-	if (xen_check_mwait())
-		cpuid_leaf1_ecx_set_mask = (1 << (X86_FEATURE_MWAIT % 32));
 }
 
 static void __init xen_init_capabilities(void)
@@ -318,6 +312,11 @@ static void __init xen_init_capabilities(void)
 
 	if (!xen_initial_domain())
 		setup_clear_cpu_cap(X86_FEATURE_ACPI);
+
+	if (xen_check_mwait())
+		setup_force_cpu_cap(X86_FEATURE_MWAIT);
+	else
+		setup_clear_cpu_cap(X86_FEATURE_MWAIT);
 }
 
 static void xen_set_debugreg(int reg, unsigned long val)
-- 
2.12.0