[Xen-devel] [PATCH 1/3] x86/spec-ctrl: add AMD SSBD LS_CFG in init print

[Brian Woods <brian.woods@xxxxxxx>]

Edit the initialization code for AMD's SSBD via the LS_CFG MSR and
enable it to pass the status to the initial spec-ctrl print_details at
boot.

Signed-off-by: Brian Woods <brian.woods@xxxxxxx>
---
 xen/arch/x86/cpu/amd.c            | 13 ++++++++++---
 xen/arch/x86/spec_ctrl.c          |  9 +++++++--
 xen/include/asm-x86/cpufeatures.h |  1 +
 xen/include/asm-x86/spec_ctrl.h   |  2 ++
 4 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/cpu/amd.c b/xen/arch/x86/cpu/amd.c
index bad5b43628..06c9e9661b 100644
--- a/xen/arch/x86/cpu/amd.c
+++ b/xen/arch/x86/cpu/amd.c
@@ -598,7 +598,7 @@ static void init_amd(struct cpuinfo_x86 *c)
         * If the user has explicitly chosen to disable Memory Disambiguation
         * to mitigiate Speculative Store Bypass, poke the appropriate MSR.
         */
-       if (opt_ssbd) {
+       if (!ssbd_amd_ls_cfg_mask) {
                int bit = -1;
 
                switch (c->x86) {
@@ -607,8 +607,15 @@ static void init_amd(struct cpuinfo_x86 *c)
                case 0x17: bit = 10; break;
                }
 
-               if (bit >= 0 && !rdmsr_safe(MSR_AMD64_LS_CFG, value)) {
-                       value |= 1ull << bit;
+               if (bit >= 0)
+                       ssbd_amd_ls_cfg_mask = 1ull << bit;
+       }
+
+       if (ssbd_amd_ls_cfg_mask && !rdmsr_safe(MSR_AMD64_LS_CFG, value)) {
+               if (!boot_cpu_has(X86_FEATURE_SSBD_AMD_LS_CFG))
+                       setup_force_cpu_cap(X86_FEATURE_SSBD_AMD_LS_CFG);
+               if (opt_ssbd) {
+                       value |= ssbd_amd_ls_cfg_mask;
                        wrmsr_safe(MSR_AMD64_LS_CFG, value);
                }
        }
diff --git a/xen/arch/x86/spec_ctrl.c b/xen/arch/x86/spec_ctrl.c
index 08e6784c4c..62e6519d93 100644
--- a/xen/arch/x86/spec_ctrl.c
+++ b/xen/arch/x86/spec_ctrl.c
@@ -50,6 +50,8 @@ bool __initdata bsp_delay_spec_ctrl;
 uint8_t __read_mostly default_xen_spec_ctrl;
 uint8_t __read_mostly default_spec_ctrl_flags;
 
+uint64_t __read_mostly ssbd_amd_ls_cfg_mask = 0ull;
+
 static int __init parse_bti(const char *s)
 {
     const char *ss;
@@ -210,10 +212,11 @@ static void __init print_details(enum ind_thunk thunk, 
uint64_t caps)
     printk("Speculative mitigation facilities:\n");
 
     /* Hardware features which pertain to speculative mitigations. */
-    printk("  Hardware features:%s%s%s%s%s%s%s%s\n",
+    printk("  Hardware features:%s%s%s%s%s%s%s%s%s\n",
            (_7d0 & cpufeat_mask(X86_FEATURE_IBRSB)) ? " IBRS/IBPB" : "",
            (_7d0 & cpufeat_mask(X86_FEATURE_STIBP)) ? " STIBP"     : "",
            (_7d0 & cpufeat_mask(X86_FEATURE_SSBD))  ? " SSBD"      : "",
+           boot_cpu_has(X86_FEATURE_SSBD_AMD_LS_CFG)? " SSBD"      : "",
            (e8b  & cpufeat_mask(X86_FEATURE_IBPB))  ? " IBPB"      : "",
            (caps & ARCH_CAPABILITIES_IBRS_ALL)      ? " IBRS_ALL"  : "",
            (caps & ARCH_CAPABILITIES_RDCL_NO)       ? " RDCL_NO"   : "",
@@ -225,7 +228,7 @@ static void __init print_details(enum ind_thunk thunk, 
uint64_t caps)
         printk("  Compiled-in support: INDIRECT_THUNK\n");
 
     /* Settings for Xen's protection, irrespective of guests. */
-    printk("  Xen settings: BTI-Thunk %s, SPEC_CTRL: %s%s, Other:%s\n",
+    printk("  Xen settings: BTI-Thunk %s, SPEC_CTRL: %s%s%s, Other:%s\n",
            thunk == THUNK_NONE      ? "N/A" :
            thunk == THUNK_RETPOLINE ? "RETPOLINE" :
            thunk == THUNK_LFENCE    ? "LFENCE" :
@@ -234,6 +237,8 @@ static void __init print_details(enum ind_thunk thunk, 
uint64_t caps)
            (default_xen_spec_ctrl & SPEC_CTRL_IBRS)  ? "IBRS+" :  "IBRS-",
            !boot_cpu_has(X86_FEATURE_SSBD)           ? "" :
            (default_xen_spec_ctrl & SPEC_CTRL_SSBD)  ? " SSBD+" : " SSBD-",
+           !boot_cpu_has(X86_FEATURE_SSBD_AMD_LS_CFG)? "" :
+           (opt_ssbd && ssbd_amd_ls_cfg_mask)        ? " SSBD+" : " SSBD-",
            opt_ibpb                                  ? " IBPB"  : "");
 
     /*
diff --git a/xen/include/asm-x86/cpufeatures.h 
b/xen/include/asm-x86/cpufeatures.h
index b90aa2d046..9383d4058b 100644
--- a/xen/include/asm-x86/cpufeatures.h
+++ b/xen/include/asm-x86/cpufeatures.h
@@ -32,3 +32,4 @@ XEN_CPUFEATURE(SC_RSB_PV,       (FSCAPINTS+0)*32+18) /* RSB 
overwrite needed for
 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_PV || 
SC_MSR_HVM) && default_xen_spec_ctrl */
+XEN_CPUFEATURE(SSBD_AMD_LS_CFG, (FSCAPINTS+0)*32+22) /* if SSBD support is 
enabled via LS_CGF MSR on AMD hardware */
diff --git a/xen/include/asm-x86/spec_ctrl.h b/xen/include/asm-x86/spec_ctrl.h
index 5b40afbab0..6aebfa9e4f 100644
--- a/xen/include/asm-x86/spec_ctrl.h
+++ b/xen/include/asm-x86/spec_ctrl.h
@@ -38,6 +38,8 @@ extern uint8_t opt_xpti;
 #define OPT_XPTI_DOM0  0x01
 #define OPT_XPTI_DOMU  0x02
 
+extern uint64_t ssbd_amd_ls_cfg_mask;
+
 static inline void init_shadow_spec_ctrl_state(void)
 {
     struct cpu_info *info = get_cpu_info();
-- 
2.11.0


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