[Xen-devel] [PATCH for-4.7/4.8] x86: Fix "x86: further CPUID handling adjustments"

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

c/s f9616884e (a backport of c/s 0d703a701 "x86/feature: Definitions for
Indirect Branch Controls") missed a CPUID adjustment when calculating the raw
featureset.  This impacts host administrator diagnostics.

Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>

c/s 62b187969 "x86: further CPUID handling adjustments" make some adjustments.
However, it breaks levelling of guests, making it impossible for the toolstack
to hide STIBP or IBPB from guests on hardware with up-to-date microcode.

Also, I don't see any link between the change and the commit message.  With
the microcode installed, STIBP and IBPB are already visible to dom0.

The only required adjustment is to force STIBP == IBRSB, which must be done
after applying the pv_featureset[] mask to the toolstack's choice of value.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
---
 xen/arch/x86/cpuid.c   | 2 +-
 xen/arch/x86/hvm/hvm.c | 8 +++++---
 xen/arch/x86/traps.c   | 8 +++++---
 3 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/cpuid.c b/xen/arch/x86/cpuid.c
index 451952c..fffcecd 100644
--- a/xen/arch/x86/cpuid.c
+++ b/xen/arch/x86/cpuid.c
@@ -113,7 +113,7 @@ static void __init calculate_raw_featureset(void)
         cpuid_count(0x7, 0, &tmp,
                     &raw_featureset[FEATURESET_7b0],
                     &raw_featureset[FEATURESET_7c0],
-                    &tmp);
+                    &raw_featureset[FEATURESET_7d0]);
     if ( max >= 0xd )
         cpuid_count(0xd, 1,
                     &raw_featureset[FEATURESET_Da1],
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index ff1c6fa..0a1d4a9 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3496,10 +3496,13 @@ void hvm_cpuid(unsigned int input, unsigned int *eax, 
unsigned int *ebx,
                      special_features[FEATURESET_7b0]);
 
             *ecx &= hvm_featureset[FEATURESET_7c0];
-
-            *edx |= cpufeat_mask(X86_FEATURE_STIBP);
             *edx &= hvm_featureset[FEATURESET_7d0];
 
+            /* Force STIBP equal to IBRSB */
+            *edx &= ~cpufeat_mask(X86_FEATURE_STIBP);
+            if ( *edx & cpufeat_mask(X86_FEATURE_IBRSB) )
+                *edx |= cpufeat_mask(X86_FEATURE_STIBP);
+
             /* Don't expose HAP-only features to non-hap guests. */
             if ( !hap_enabled(d) )
             {
@@ -3657,7 +3660,6 @@ void hvm_cpuid(unsigned int input, unsigned int *eax, 
unsigned int *ebx,
         hvm_cpuid(0x80000001, NULL, NULL, NULL, &_edx);
         *eax |= (_edx & cpufeat_mask(X86_FEATURE_LM) ? vaddr_bits : 32) << 8;
 
-        *ebx |= cpufeat_mask(X86_FEATURE_IBPB);
         *ebx &= hvm_featureset[FEATURESET_e8b];
         break;
     }
diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 0f34b21..da26749 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -1088,10 +1088,13 @@ void pv_cpuid(struct cpu_user_regs *regs)
                   special_features[FEATURESET_7b0]);
 
             c &= pv_featureset[FEATURESET_7c0];
-
-            d |= cpufeat_mask(X86_FEATURE_STIBP);
             d &= pv_featureset[FEATURESET_7d0];
 
+            /* Force STIBP equal to IBRSB */
+            d &= ~cpufeat_mask(X86_FEATURE_STIBP);
+            if ( d & cpufeat_mask(X86_FEATURE_IBRSB) )
+                d |= cpufeat_mask(X86_FEATURE_STIBP);
+
             if ( !is_pvh_domain(currd) )
             {
                 /*
@@ -1188,7 +1191,6 @@ void pv_cpuid(struct cpu_user_regs *regs)
 
     case 0x80000008:
         a = paddr_bits | (vaddr_bits << 8);
-        b |= cpufeat_mask(X86_FEATURE_IBPB);
         b &= pv_featureset[FEATURESET_e8b];
         break;
 
-- 
2.1.4


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