1 files changed, 71 insertions, 0 deletions
diff --git a/main/xen/0006-x86-spec_ctrl-Elide-MSR_SPEC_CTRL-handling-in-idle-c.patch b/main/xen/0006-x86-spec_ctrl-Elide-MSR_SPEC_CTRL-handling-in-idle-c.patch
new file mode 100644
index 0000000000..f771e545d5
--- /dev/null
+++ b/main/xen/0006-x86-spec_ctrl-Elide-MSR_SPEC_CTRL-handling-in-idle-c.patch
@@ -0,0 +1,71 @@
+From 12dec36f81cdd8aecc5388f983884cbb4e437ce8 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 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
+