[Xen-devel] [PATCH 1/2] x86/vtx: Corrections to BFD93 errata workaround

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

At the time of fixing c/s 20f1976b44, no obvious errata had been published,
and BDF14 looked like the most obvious candidate.  Subsequently, BDF93 has
been published and it is obviously this.

The erratum states that LER_TO_LIP is the only affected MSR.  The provisional
fix in Xen adjusted LER_FROM_LIP, but this is not correct.  The FROM MSRs are
intended to have TSX metadata, and for steppings with TSX enabled, it will
corrupt the value the guest sees, while for parts with TSX disabled, it is
redundant with FIXUP_TSX.  Drop the LER_FROM_LIP adjustment.

Replace BDF14 references with BDF93, drop the redundant 'bdw_erratum_' prefix,
and use an Intel vendor check, as other vendors implement VT-x.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Jun Nakajima <jun.nakajima@xxxxxxxxx>
CC: Kevin Tian <kevin.tian@xxxxxxxxx>
CC: Juergen Gross <jgross@xxxxxxxx>
---
 xen/arch/x86/hvm/vmx/vmx.c | 45 +++++++++++++++++++++------------------------
 1 file changed, 21 insertions(+), 24 deletions(-)

diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
index 535e0384fe..32d289ce06 100644
--- a/xen/arch/x86/hvm/vmx/vmx.c
+++ b/xen/arch/x86/hvm/vmx/vmx.c
@@ -2369,7 +2369,7 @@ static void pi_notification_interrupt(struct 
cpu_user_regs *regs)
 }
 
 static void __init lbr_tsx_fixup_check(void);
-static void __init bdw_erratum_bdf14_fixup_check(void);
+static void __init bdf93_fixup_check(void);
 
 const struct hvm_function_table * __init start_vmx(void)
 {
@@ -2438,7 +2438,7 @@ const struct hvm_function_table * __init start_vmx(void)
     setup_vmcs_dump();
 
     lbr_tsx_fixup_check();
-    bdw_erratum_bdf14_fixup_check();
+    bdf93_fixup_check();
 
     return &vmx_function_table;
 }
@@ -2722,11 +2722,11 @@ enum
 
 #define LBR_MSRS_INSERTED      (1u << 0)
 #define LBR_FIXUP_TSX          (1u << 1)
-#define LBR_FIXUP_BDF14        (1u << 2)
-#define LBR_FIXUP_MASK         (LBR_FIXUP_TSX | LBR_FIXUP_BDF14)
+#define LBR_FIXUP_BDF93        (1u << 2)
+#define LBR_FIXUP_MASK         (LBR_FIXUP_TSX | LBR_FIXUP_BDF93)
 
 static bool __read_mostly lbr_tsx_fixup_needed;
-static bool __read_mostly bdw_erratum_bdf14_fixup_needed;
+static bool __read_mostly bdf93_fixup_needed;
 static uint32_t __read_mostly lbr_from_start;
 static uint32_t __read_mostly lbr_from_end;
 static uint32_t __read_mostly lbr_lastint_from;
@@ -2763,11 +2763,18 @@ static void __init lbr_tsx_fixup_check(void)
     }
 }
 
-static void __init bdw_erratum_bdf14_fixup_check(void)
+static void __init bdf93_fixup_check(void)
 {
-    /* Broadwell E5-2600 v4 processors need to work around erratum BDF14. */
-    if ( boot_cpu_data.x86 == 6 && boot_cpu_data.x86_model == 79 )
-        bdw_erratum_bdf14_fixup_needed = true;
+    /*
+     * Broadwell erratum BDF93:
+     *
+     * Reads from MSR_LER_TO_LIP (MSR 1DEH) may return values for bits[63:61]
+     * that are not equal to bit[47].  Attempting to context switch this value
+     * may cause a #GP.  Software should sign extend the MSR.
+     */
+    if ( boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
+         boot_cpu_data.x86 == 6 && boot_cpu_data.x86_model == 0x4f )
+        bdf93_fixup_needed = true;
 }
 
 static int is_last_branch_msr(u32 ecx)
@@ -3128,8 +3135,8 @@ static int vmx_msr_write_intercept(unsigned int msr, 
uint64_t msr_content)
             v->arch.hvm.vmx.lbr_flags |= LBR_MSRS_INSERTED;
             if ( lbr_tsx_fixup_needed )
                 v->arch.hvm.vmx.lbr_flags |= LBR_FIXUP_TSX;
-            if ( bdw_erratum_bdf14_fixup_needed )
-                v->arch.hvm.vmx.lbr_flags |= LBR_FIXUP_BDF14;
+            if ( bdf93_fixup_needed )
+                v->arch.hvm.vmx.lbr_flags |= LBR_FIXUP_BDF93;
         }
 
         __vmwrite(GUEST_IA32_DEBUGCTL, msr_content);
@@ -4148,20 +4155,10 @@ static void sign_extend_msr(struct vcpu *v, u32 msr, 
int type)
         entry->data = canonicalise_addr(entry->data);
 }
 
-static void bdw_erratum_bdf14_fixup(void)
+static void bdf93_fixup(void)
 {
     struct vcpu *curr = current;
 
-    /*
-     * Occasionally, on certain Broadwell CPUs MSR_IA32_LASTINTTOIP has
-     * been observed to have the top three bits corrupted as though the
-     * MSR is using the LBR_FORMAT_EIP_FLAGS_TSX format. This is
-     * incorrect and causes a vmentry failure -- the MSR should contain
-     * an offset into the current code segment. This is assumed to be
-     * erratum BDF14. Fix up MSR_IA32_LASTINT{FROM,TO}IP by
-     * sign-extending into bits 48:63.
-     */
-    sign_extend_msr(curr, MSR_IA32_LASTINTFROMIP, VMX_MSR_GUEST);
     sign_extend_msr(curr, MSR_IA32_LASTINTTOIP, VMX_MSR_GUEST);
 }
 
@@ -4171,8 +4168,8 @@ static void lbr_fixup(void)
 
     if ( curr->arch.hvm.vmx.lbr_flags & LBR_FIXUP_TSX )
         lbr_tsx_fixup();
-    if ( curr->arch.hvm.vmx.lbr_flags & LBR_FIXUP_BDF14 )
-        bdw_erratum_bdf14_fixup();
+    if ( curr->arch.hvm.vmx.lbr_flags & LBR_FIXUP_BDF93 )
+        bdf93_fixup();
 }
 
 /* Returns false if the vmentry has to be restarted */
-- 
2.11.0


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