From 811fcf5137abdcd5b9ea7e5212098adb5bedae0f Mon Sep 17 00:00:00 2001
From: Andrew Cooper <andrew.cooper3@citrix.com>
Date: Mon, 7 May 2018 14:06:16 +0100
Subject: [PATCH] x86/spec_ctrl: Elide MSR_SPEC_CTRL handling in idle context
when possible
If Xen is virtualising MSR_SPEC_CTRL handling for guests, but using 0 as its
own MSR_SPEC_CTRL value, spec_ctrl_{enter,exit}_idle() need not write to the
MSR.
Requested-by: Jan Beulich <JBeulich@suse.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Juergen Gross <jgross@suse.com>
(cherry picked from commit 94df6e8588e35cc2028ccb3fd2921c6e6360605e)
---
xen/arch/x86/spec_ctrl.c | 4 ++++
xen/include/asm-x86/cpufeatures.h | 1 +
xen/include/asm-x86/spec_ctrl.h | 4 ++--
3 files changed, 7 insertions(+), 2 deletions(-)
diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index 015a9e2..55ef79f 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -327,6 +327,10 @@ void __init init_speculation_mitigations(void)
/* (Re)init BSP state now that default_spec_ctrl_flags has been calculated. */
init_shadow_spec_ctrl_state();
+ /* If Xen is using any MSR_SPEC_CTRL settings, adjust the idle path. */
+ if ( default_xen_spec_ctrl )
+ setup_force_cpu_cap(X86_FEATURE_SC_MSR_IDLE);
+
print_details(thunk, caps);
}
diff --git a/xen/include/asm-x86/cpufeatures.h b/xen/include/asm-x86/cpufeatures.h
index f9aa5d7..32b7f04 100644
--- a/xen/include/asm-x86/cpufeatures.h
+++ b/xen/include/asm-x86/cpufeatures.h
@@ -30,3 +30,4 @@ XEN_CPUFEATURE(SC_MSR, (FSCAPINTS+0)*32+16) /* MSR_SPEC_CTRL used by Xe
XEN_CPUFEATURE(SC_RSB_PV, (FSCAPINTS+0)*32+18) /* RSB overwrite needed for PV */
XEN_CPUFEATURE(SC_RSB_HVM, (FSCAPINTS+0)*32+19) /* RSB overwrite needed for HVM */
XEN_CPUFEATURE(NO_XPTI, (FSCAPINTS+0)*32+20) /* XPTI mitigation not in use */
+XEN_CPUFEATURE(SC_MSR_IDLE, (FSCAPINTS+0)*32+21) /* SC_MSR && default_xen_spec_ctrl */
diff --git a/xen/include/asm-x86/spec_ctrl.h b/xen/include/asm-x86/spec_ctrl.h
index 7d7c42e..77f92ba 100644
--- a/xen/include/asm-x86/spec_ctrl.h
+++ b/xen/include/asm-x86/spec_ctrl.h
@@ -52,7 +52,7 @@ static always_inline void spec_ctrl_enter_idle(struct cpu_info *info)
barrier();
info->spec_ctrl_flags |= SCF_use_shadow;
barrier();
- asm volatile ( ALTERNATIVE(ASM_NOP3, "wrmsr", X86_FEATURE_SC_MSR)
+ asm volatile ( ALTERNATIVE(ASM_NOP3, "wrmsr", X86_FEATURE_SC_MSR_IDLE)
:: "a" (val), "c" (MSR_SPEC_CTRL), "d" (0) : "memory" );
}
@@ -67,7 +67,7 @@ static always_inline void spec_ctrl_exit_idle(struct cpu_info *info)
*/
info->spec_ctrl_flags &= ~SCF_use_shadow;
barrier();
- asm volatile ( ALTERNATIVE(ASM_NOP3, "wrmsr", X86_FEATURE_SC_MSR)
+ asm volatile ( ALTERNATIVE(ASM_NOP3, "wrmsr", X86_FEATURE_SC_MSR_IDLE)
:: "a" (val), "c" (MSR_SPEC_CTRL), "d" (0) : "memory" );
}
--
2.1.4
|
