[PATCH 2/5] x86/lbr: enable hypervisor LER with arch LBR

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

CPUs having no model-specific LBRs don't implement DEBUGCTLMSR.LBR
and LBRs can only be enabled if the processor supports architectural
LBRs.

Split the logic to enable LBRs into a separate function and expand the
logic to also implement support for arch LBRs if model-specific LBRs
are not supported.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/include/asm/msr-index.h        | 18 +++++++++++++
 xen/arch/x86/traps.c                        | 29 ++++++++++++++++++---
 xen/include/public/arch-x86/cpufeatureset.h |  1 +
 3 files changed, 45 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/include/asm/msr-index.h 
b/xen/arch/x86/include/asm/msr-index.h
index 3e038db618..7b08e1804b 100644
--- a/xen/arch/x86/include/asm/msr-index.h
+++ b/xen/arch/x86/include/asm/msr-index.h
@@ -139,6 +139,24 @@
 #define  PASID_PASID_MASK                   0x000fffff
 #define  PASID_VALID                        (_AC(1, ULL) << 31)
 
+#define MSR_ARCH_LBR_CTL                    0x000014ce
+#define  ARCH_LBR_CTL_LBREN                 (_AC(1, ULL) <<  0)
+#define  ARCH_LBR_CTL_OS                    (_AC(1, ULL) <<  1)
+#define  ARCH_LBR_CTL_COND                  (_AC(1, ULL) << 16)
+#define  ARCH_LBR_CTL_NEAR_REL_JMP          (_AC(1, ULL) << 17)
+#define  ARCH_LBR_CTL_NEAR_IND_JMP          (_AC(1, ULL) << 18)
+#define  ARCH_LBR_CTL_NEAR_REL_CALL         (_AC(1, ULL) << 19)
+#define  ARCH_LBR_CTL_NEAR_IND_CALL         (_AC(1, ULL) << 20)
+#define  ARCH_LBR_CTL_NEAR_RET              (_AC(1, ULL) << 21)
+#define  ARCH_LBR_CTL_OTHER_BRANCH          (_AC(1, ULL) << 22)
+#define  ARCH_LBR_CTL_RECORD_ALL            (ARCH_LBR_CTL_COND | \
+                                             ARCH_LBR_CTL_NEAR_REL_JMP | \
+                                             ARCH_LBR_CTL_NEAR_IND_JMP | \
+                                             ARCH_LBR_CTL_NEAR_REL_CALL | \
+                                             ARCH_LBR_CTL_NEAR_IND_CALL | \
+                                             ARCH_LBR_CTL_NEAR_RET | \
+                                             ARCH_LBR_CTL_OTHER_BRANCH)
+
 #define MSR_EFER                            0xc0000080 /* Extended Feature 
Enable Register */
 #define  EFER_SCE                           (_AC(1, ULL) <<  0) /* SYSCALL 
Enable */
 #define  EFER_LME                           (_AC(1, ULL) <<  8) /* Long Mode 
Enable */
diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 4c38f6c015..133348d9f9 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -1963,6 +1963,29 @@ void do_device_not_available(struct cpu_user_regs *regs)
 #endif
 }
 
+static bool enable_lbr(void)
+{
+    uint64_t debugctl;
+
+    wrmsrl(MSR_IA32_DEBUGCTLMSR, IA32_DEBUGCTLMSR_LBR);
+    rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
+    if ( !(debugctl & IA32_DEBUGCTLMSR_LBR) )
+    {
+        /*
+         * CPUs with no model-specific LBRs always return DEBUGCTLMSR.LBR
+         * == 0, attempt to set arch LBR if available.
+         */
+        if ( !boot_cpu_has(X86_FEATURE_ARCH_LBR) )
+            return false;
+
+        /* Note that LASTINT{FROMIP,TOIP} matches LER_{FROM_IP,TO_IP} */
+        wrmsrl(MSR_ARCH_LBR_CTL, ARCH_LBR_CTL_LBREN | ARCH_LBR_CTL_OS |
+                                 ARCH_LBR_CTL_RECORD_ALL);
+    }
+
+    return true;
+}
+
 void do_debug(struct cpu_user_regs *regs)
 {
     unsigned long dr6;
@@ -1997,7 +2020,7 @@ void do_debug(struct cpu_user_regs *regs)
 
     /* #DB automatically disabled LBR.  Reinstate it if debugging Xen. */
     if ( cpu_has_xen_lbr )
-        wrmsrl(MSR_IA32_DEBUGCTLMSR, IA32_DEBUGCTLMSR_LBR);
+        enable_lbr();
 
     if ( !guest_mode(regs) )
     {
@@ -2179,8 +2202,8 @@ void percpu_traps_init(void)
     if ( !ler_msr && (ler_msr = calc_ler_msr()) )
         setup_force_cpu_cap(X86_FEATURE_XEN_LBR);
 
-    if ( cpu_has_xen_lbr )
-        wrmsrl(MSR_IA32_DEBUGCTLMSR, IA32_DEBUGCTLMSR_LBR);
+    if ( cpu_has_xen_lbr && !enable_lbr() )
+        printk(XENLOG_ERR "CPU#%u: failed to enable LBR\n", 
smp_processor_id());
 }
 
 void __init init_idt_traps(void)
diff --git a/xen/include/public/arch-x86/cpufeatureset.h 
b/xen/include/public/arch-x86/cpufeatureset.h
index 9cee4b439e..cd6409f9f3 100644
--- a/xen/include/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -280,6 +280,7 @@ XEN_CPUFEATURE(RTM_ALWAYS_ABORT, 9*32+11) /*! June 2021 TSX 
defeaturing in micro
 XEN_CPUFEATURE(TSX_FORCE_ABORT, 9*32+13) /* MSR_TSX_FORCE_ABORT.RTM_ABORT */
 XEN_CPUFEATURE(SERIALIZE,     9*32+14) /*A  SERIALIZE insn */
 XEN_CPUFEATURE(TSXLDTRK,      9*32+16) /*a  TSX load tracking suspend/resume 
insns */
+XEN_CPUFEATURE(ARCH_LBR,      9*32+19) /*   Intel ARCH LBR */
 XEN_CPUFEATURE(CET_IBT,       9*32+20) /*   CET - Indirect Branch Tracking */
 XEN_CPUFEATURE(IBRSB,         9*32+26) /*A  IBRS and IBPB support (used by 
Intel) */
 XEN_CPUFEATURE(STIBP,         9*32+27) /*A  STIBP */
-- 
2.36.0