[PATCH v2 2/3] x86: Expose Automatic IBRS to guests

[Alejandro Vallejo <alejandro.vallejo@cloud.com>]

Expose AutoIBRS to HVM guests. EFER is swapped by VMRUN, so Xen only has to
make sure writes to EFER.AIBRSE are gated on the feature being exposed.

Also hide EFER.AIBRSE from PV guests as they have no say in the matter.

Signed-off-by: Alejandro Vallejo <alejandro.vallejo@cloud.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
v2:
  * Moved to patch2 from v1/patch3
---
 xen/arch/x86/hvm/hvm.c                      | 3 +++
 xen/arch/x86/include/asm/msr-index.h        | 3 ++-
 xen/arch/x86/pv/emul-priv-op.c              | 4 ++--
 xen/include/public/arch-x86/cpufeatureset.h | 2 +-
 4 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index d7d31b5393..2d6e4bb9c6 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -936,6 +936,9 @@ const char *hvm_efer_valid(const struct vcpu *v, uint64_t value,
     if ( (value & EFER_FFXSE) && !p->extd.ffxsr )
         return "FFXSE without feature";
 
+    if ( (value & EFER_AIBRSE) && !p->extd.auto_ibrs )
+        return "AutoIBRS without feature";
+
     return NULL;
 }
 
diff --git a/xen/arch/x86/include/asm/msr-index.h b/xen/arch/x86/include/asm/msr-index.h
index 73d0af2615..49cb334c61 100644
--- a/xen/arch/x86/include/asm/msr-index.h
+++ b/xen/arch/x86/include/asm/msr-index.h
@@ -178,7 +178,8 @@
 #define  EFER_AIBRSE                        (_AC(1, ULL) << 21) /* Automatic IBRS Enable */
 
 #define EFER_KNOWN_MASK \
-    (EFER_SCE | EFER_LME | EFER_LMA | EFER_NXE | EFER_SVME | EFER_FFXSE)
+    (EFER_SCE | EFER_LME | EFER_LMA | EFER_NXE | EFER_SVME | EFER_FFXSE | \
+     EFER_AIBRSE)
 
 #define MSR_STAR                            0xc0000081 /* legacy mode SYSCALL target */
 #define MSR_LSTAR                           0xc0000082 /* long mode SYSCALL target */
diff --git a/xen/arch/x86/pv/emul-priv-op.c b/xen/arch/x86/pv/emul-priv-op.c
index 8a4ef9c35e..142bc4818c 100644
--- a/xen/arch/x86/pv/emul-priv-op.c
+++ b/xen/arch/x86/pv/emul-priv-op.c
@@ -853,8 +853,8 @@ static uint64_t guest_efer(const struct domain *d)
 {
     uint64_t val;
 
-    /* Hide unknown bits, and unconditionally hide SVME from guests. */
-    val = read_efer() & EFER_KNOWN_MASK & ~EFER_SVME;
+    /* Hide unknown bits, and unconditionally hide SVME and AIBRSE from guests. */
+    val = read_efer() & EFER_KNOWN_MASK & ~(EFER_SVME | EFER_AIBRSE);
     /*
      * Hide the 64-bit features from 32-bit guests.  SCE has
      * vendor-dependent behaviour.
diff --git a/xen/include/public/arch-x86/cpufeatureset.h b/xen/include/public/arch-x86/cpufeatureset.h
index 3ac144100e..51d737a125 100644
--- a/xen/include/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -287,7 +287,7 @@ XEN_CPUFEATURE(AVX_IFMA,     10*32+23) /*A  AVX-IFMA Instructions */
 /* AMD-defined CPU features, CPUID level 0x80000021.eax, word 11 */
 XEN_CPUFEATURE(LFENCE_DISPATCH,    11*32+ 2) /*A  LFENCE always serializing */
 XEN_CPUFEATURE(NSCB,               11*32+ 6) /*A  Null Selector Clears Base (and limit too) */
-XEN_CPUFEATURE(AUTO_IBRS,          11*32+ 8) /*   HW can handle IBRS on its own */
+XEN_CPUFEATURE(AUTO_IBRS,          11*32+ 8) /*S  HW can handle IBRS on its own */
 XEN_CPUFEATURE(CPUID_USER_DIS,     11*32+17) /*   CPUID disable for CPL > 0 software */
 
 /* Intel-defined CPU features, CPUID level 0x00000007:1.ebx, word 12 */
-- 
2.34.1