x86/cpuid: Enable MSR_SPEC_CTRL in SVM guests by default

With all other pieces in place, MSR_SPEC_CTRL is fully working for HVM guests.

Update the CPUID derivation logic (both PV and HVM to avoid losing subtle
changes), drop the MSR intercept, and explicitly enable the CPUID bits for HVM
guests.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
index b5af48324aef1bd736f53a226bd83b51dd75a852..e24dd283e7613d31befe9c6cb3d724078d4346aa 100644 (file)
--- a/xen/arch/x86/cpuid.c
+++ b/xen/arch/x86/cpuid.c
@@ -433,6 +433,8 @@ static void __init guest_common_feature_adjustments(uint32_t *fs)
      */
     if ( test_bit(X86_FEATURE_IBRSB, fs) )
         __set_bit(X86_FEATURE_STIBP, fs);
+    if ( test_bit(X86_FEATURE_IBRS, fs) )
+        __set_bit(X86_FEATURE_AMD_STIBP, fs);
 
     /*
      * On hardware which supports IBRS/IBPB, we can offer IBPB independently
@@ -456,11 +458,14 @@ static void __init calculate_pv_max_policy(void)
         pv_featureset[i] &= pv_max_featuremask[i];
 
     /*
-     * If Xen isn't virtualising MSR_SPEC_CTRL for PV guests because of
-     * administrator choice, hide the feature.
+     * If Xen isn't virtualising MSR_SPEC_CTRL for PV guests (functional
+     * availability, or admin choice), hide the feature.
      */
     if ( !boot_cpu_has(X86_FEATURE_SC_MSR_PV) )
+    {
         __clear_bit(X86_FEATURE_IBRSB, pv_featureset);
+        __clear_bit(X86_FEATURE_IBRS, pv_featureset);
+    }
 
     guest_common_feature_adjustments(pv_featureset);
 
@@ -530,11 +535,14 @@ static void __init calculate_hvm_max_policy(void)
         __set_bit(X86_FEATURE_SEP, hvm_featureset);
 
     /*
-     * If Xen isn't virtualising MSR_SPEC_CTRL for HVM guests because of
-     * administrator choice, hide the feature.
+     * If Xen isn't virtualising MSR_SPEC_CTRL for HVM guests (functional
+     * availability, or admin choice), hide the feature.
      */
     if ( !boot_cpu_has(X86_FEATURE_SC_MSR_HVM) )
+    {
         __clear_bit(X86_FEATURE_IBRSB, hvm_featureset);
+        __clear_bit(X86_FEATURE_IBRS, hvm_featureset);
+    }
 
     /*
      * With VT-x, some features are only supported by Xen if dedicated

diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 5459fbf4d4b59b8bd92bfa46149dd3a21126b1a5..c4ce3f75ab748e71be95ffd286d7d631fb461984 100644 (file)
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -606,6 +606,10 @@ static void svm_cpuid_policy_changed(struct vcpu *v)
 
     vmcb_set_exception_intercepts(vmcb, bitmap);
 
+    /* Give access to MSR_SPEC_CTRL if the guest has been told about it. */
+    svm_intercept_msr(v, MSR_SPEC_CTRL,
+                      cp->extd.ibrs ? MSR_INTERCEPT_NONE : MSR_INTERCEPT_RW);
+
     /* Give access to MSR_PRED_CMD if the guest has been told about it. */
     svm_intercept_msr(v, MSR_PRED_CMD,
                       cp->extd.ibpb ? MSR_INTERCEPT_NONE : MSR_INTERCEPT_RW);

diff --git a/xen/include/public/arch-x86/cpufeatureset.h b/xen/include/public/arch-x86/cpufeatureset.h
index fd8ab25723043cf14030e435312fc7ed3f8e9650..957df23b65f25af336af3f8722a62bad97dba64a 100644 (file)
--- a/xen/include/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -256,18 +256,18 @@ XEN_CPUFEATURE(CLZERO,        8*32+ 0) /*A  CLZERO instruction */
 XEN_CPUFEATURE(RSTR_FP_ERR_PTRS, 8*32+ 2) /*A  (F)X{SAVE,RSTOR} always saves/restores FPU Error pointers */
 XEN_CPUFEATURE(WBNOINVD,      8*32+ 9) /*   WBNOINVD instruction */
 XEN_CPUFEATURE(IBPB,          8*32+12) /*A  IBPB support only (no IBRS, used by AMD) */
-XEN_CPUFEATURE(IBRS,          8*32+14) /*   MSR_SPEC_CTRL.IBRS */
-XEN_CPUFEATURE(AMD_STIBP,     8*32+15) /*   MSR_SPEC_CTRL.STIBP */
-XEN_CPUFEATURE(IBRS_ALWAYS,   8*32+16) /*   IBRS preferred always on */
-XEN_CPUFEATURE(STIBP_ALWAYS,  8*32+17) /*   STIBP preferred always on */
-XEN_CPUFEATURE(IBRS_FAST,     8*32+18) /*   IBRS preferred over software options */
-XEN_CPUFEATURE(IBRS_SAME_MODE, 8*32+19) /*   IBRS provides same-mode protection */
+XEN_CPUFEATURE(IBRS,          8*32+14) /*S  MSR_SPEC_CTRL.IBRS */
+XEN_CPUFEATURE(AMD_STIBP,     8*32+15) /*S  MSR_SPEC_CTRL.STIBP */
+XEN_CPUFEATURE(IBRS_ALWAYS,   8*32+16) /*S  IBRS preferred always on */
+XEN_CPUFEATURE(STIBP_ALWAYS,  8*32+17) /*S  STIBP preferred always on */
+XEN_CPUFEATURE(IBRS_FAST,     8*32+18) /*S  IBRS preferred over software options */
+XEN_CPUFEATURE(IBRS_SAME_MODE, 8*32+19) /*S  IBRS provides same-mode protection */
 XEN_CPUFEATURE(NO_LMSL,       8*32+20) /*S  EFER.LMSLE no longer supported. */
 XEN_CPUFEATURE(AMD_PPIN,      8*32+23) /*   Protected Processor Inventory Number */
-XEN_CPUFEATURE(AMD_SSBD,      8*32+24) /*   MSR_SPEC_CTRL.SSBD available */
+XEN_CPUFEATURE(AMD_SSBD,      8*32+24) /*S  MSR_SPEC_CTRL.SSBD available */
 XEN_CPUFEATURE(VIRT_SSBD,     8*32+25) /*   MSR_VIRT_SPEC_CTRL.SSBD */
 XEN_CPUFEATURE(SSB_NO,        8*32+26) /*A  Hardware not vulnerable to SSB */
-XEN_CPUFEATURE(PSFD,          8*32+28) /*   MSR_SPEC_CTRL.PSFD */
+XEN_CPUFEATURE(PSFD,          8*32+28) /*S  MSR_SPEC_CTRL.PSFD */
 
 /* Intel-defined CPU features, CPUID level 0x00000007:0.edx, word 9 */
 XEN_CPUFEATURE(AVX512_4VNNIW, 9*32+ 2) /*A  AVX512 Neural Network Instructions */

diff --git a/xen/tools/gen-cpuid.py b/xen/tools/gen-cpuid.py
index 470cd76d1c52218964073823ef92215d706893b0..39c8b0c77465c56dd86917534cbd2f41e5b496c0 100755 (executable)
--- a/xen/tools/gen-cpuid.py
+++ b/xen/tools/gen-cpuid.py
@@ -277,16 +277,20 @@ def crunch_numbers(state):
         # The features:
         #   * Single Thread Indirect Branch Predictors
         #   * Speculative Store Bypass Disable
+        #   * Predictive Store Forward Disable
         #
-        # enumerate new bits in MSR_SPEC_CTRL, which is enumerated by Indirect
-        # Branch Restricted Speculation/Indirect Branch Prediction Barrier.
+        # enumerate new bits in MSR_SPEC_CTRL, and technically enumerate
+        # MSR_SPEC_CTRL itself.  AMD further enumerates hints to guide OS
+        # behaviour.
         #
-        # In practice, these features also enumerate the presense of
-        # MSR_SPEC_CTRL.  However, no real hardware will exist with SSBD but
-        # not IBRSB, and we pass this MSR directly to guests.  Treating them
+        # However, no real hardware will exist with e.g. SSBD but not
+        # IBRSB/IBRS, and we pass this MSR directly to guests.  Treating them
         # as dependent features simplifies Xen's logic, and prevents the guest
         # from seeing implausible configurations.
         IBRSB: [STIBP, SSBD],
+        IBRS: [AMD_STIBP, AMD_SSBD, PSFD,
+               IBRS_ALWAYS, IBRS_FAST, IBRS_SAME_MODE],
+        AMD_STIBP: [STIBP_ALWAYS],
 
         # In principle the TSXLDTRK insns could also be considered independent.
         RTM: [TSXLDTRK],