From 12dec36f81cdd8aecc5388f983884cbb4e437ce8 Mon Sep 17 00:00:00 2001 From: Andrew Cooper 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 Signed-off-by: Andrew Cooper Reviewed-by: Wei Liu Reviewed-by: Jan Beulich Release-acked-by: Juergen Gross (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 1353fe5..f419c36 100644 --- a/xen/include/asm-x86/cpufeatures.h +++ b/xen/include/asm-x86/cpufeatures.h @@ -32,3 +32,4 @@ XEN_CPUFEATURE(SC_MSR, (FSCAPINTS+0)*32+18) /* MSR_SPEC_CTRL used by Xe XEN_CPUFEATURE(SC_RSB_PV, (FSCAPINTS+0)*32+20) /* RSB overwrite needed for PV */ XEN_CPUFEATURE(SC_RSB_HVM, (FSCAPINTS+0)*32+21) /* RSB overwrite needed for HVM */ XEN_CPUFEATURE(NO_XPTI, (FSCAPINTS+0)*32+22) /* XPTI mitigation not in use */ +XEN_CPUFEATURE(SC_MSR_IDLE, (FSCAPINTS+0)*32+23) /* 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