[Xen-devel] [PATCH for-4.11] x86/pv: Unconditionally hide EFER.SVME from PV guests

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

We don't advertise SVM in CPUID so a PV guest shouldn't be under the
impression that it can use SVM functionality, but despite this, it really
shouldn't see SVME set when reading EFER.

Introduce EFER_KNOWN_MASK to whitelist the features Xen knows about, and use
this to clamp the guests view.

Take the opportunity to reuse the mask to simplify svm_vmcb_isvalid(), and
change "undefined" to "unknown" in the print message, as there is at least
EFER.TCE (Translation Cache Extension) defined but unknown to Xen.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
CC: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
CC: Brian Woods <brian.woods@xxxxxxx>
CC: Juergen Gross <jgross@xxxxxxxx>

Arguably, this wants backporting to the stable trees, so should be considered
for 4.11 at this point.
---
 xen/arch/x86/hvm/svm/svmdebug.c | 5 ++---
 xen/arch/x86/pv/emul-priv-op.c  | 4 +++-
 xen/include/asm-x86/msr-index.h | 3 +++
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/svmdebug.c b/xen/arch/x86/hvm/svm/svmdebug.c
index 6c215d1..d35e405 100644
--- a/xen/arch/x86/hvm/svm/svmdebug.c
+++ b/xen/arch/x86/hvm/svm/svmdebug.c
@@ -133,9 +133,8 @@ bool svm_vmcb_isvalid(const char *from, const struct 
vmcb_struct *vmcb,
         PRINTF("DR7: bits [63:32] are not zero (%#"PRIx64")\n",
                vmcb_get_dr7(vmcb));
 
-    if ( efer & ~(EFER_SCE | EFER_LME | EFER_LMA | EFER_NX | EFER_SVME |
-                  EFER_LMSLE | EFER_FFXSE) )
-        PRINTF("EFER: undefined bits are not zero (%#"PRIx64")\n", efer);
+    if ( efer & ~EFER_KNOWN_MASK )
+        PRINTF("EFER: unknown bits are not zero (%#"PRIx64")\n", efer);
 
     if ( hvm_efer_valid(v, efer, -1) )
         PRINTF("EFER: %s (%"PRIx64")\n", hvm_efer_valid(v, efer, -1), efer);
diff --git a/xen/arch/x86/pv/emul-priv-op.c b/xen/arch/x86/pv/emul-priv-op.c
index 15f42b3..8293f31 100644
--- a/xen/arch/x86/pv/emul-priv-op.c
+++ b/xen/arch/x86/pv/emul-priv-op.c
@@ -867,7 +867,9 @@ static int read_msr(unsigned int reg, uint64_t *val,
         return X86EMUL_OKAY;
 
     case MSR_EFER:
-        *val = read_efer();
+        /* Hide unknown bits, and unconditionally hide SVME from guests. */
+        *val = read_efer() & EFER_KNOWN_MASK & ~EFER_SVME;
+        /* Hide the 64-bit features from 32-bit guests. */
         if ( is_pv_32bit_domain(currd) )
             *val &= ~(EFER_LME | EFER_LMA | EFER_LMSLE);
         return X86EMUL_OKAY;
diff --git a/xen/include/asm-x86/msr-index.h b/xen/include/asm-x86/msr-index.h
index c9f44eb..6d94d65 100644
--- a/xen/include/asm-x86/msr-index.h
+++ b/xen/include/asm-x86/msr-index.h
@@ -31,6 +31,9 @@
 #define EFER_LMSLE             (1<<_EFER_LMSLE)
 #define EFER_FFXSE             (1<<_EFER_FFXSE)
 
+#define EFER_KNOWN_MASK                (EFER_SCE | EFER_LME | EFER_LMA | 
EFER_NX | \
+                                EFER_SVME | EFER_LMSLE | EFER_FFXSE)
+
 /* Speculation Controls. */
 #define MSR_SPEC_CTRL                  0x00000048
 #define SPEC_CTRL_IBRS                 (_AC(1, ULL) << 0)
-- 
2.1.4


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