[PATCH v2] xen/arm: Hide PMU registers from the guest, when the vPMU feature is disabled.

[Hirokazu Takahashi <taka@xxxxxxxxxxxxx>]

On ARMv8.4-A and newer platforms, booting Dom0 Linux with ACPI enabled
causes the domain to probe advanced PMU feature based on system ID
register ID_AA64DFR0_EL1.During this probe, Linux accesses PMMIR_EL1,
which causes unhandled register traps and crashes the domain.

To address this issue, I implement the following:

- Hide PMU registers from a guest domain when its vPMU feature is
  disabled.
- Proactively make SPE, TRBE, BRBE, and Trace Extensions inaccessible
  to guest domains, as they could potentially cause similar issues.
- Add emulation for PMMIR_EL1 register accesses performed by a guest
  domain when vPMU is enabled. However, similar to reads from other
  PMU registers, the read value returns zero (note that this is a
  temporary implementation).
- Emulation for PMSS (PMU Snapshot) register accesses is not yet
  implemented, because PMSS support is not available in
  qemu-system-aarch64 and could not be verified.

Fixes: 07b9acea116e "xen/arm: Add handler for ID registers on arm64"
Fixes: 3669a1cb9598 "xen/arm: create a cpuinfo structure for guest"
Signed-off-by: Hirokazu Takahashi <taka@xxxxxxxxxxxxx>
---
Changes in v2:
 * Instead of unconditionally hiding the PMU feature from guests,
   we now determine whether to expose PMU to a guest domain based on
   its configuration.

 xen/arch/arm/arm64/vsysreg.c          | 31 +++++++++++++++++++++++++--
 xen/arch/arm/cpufeature.c             |  8 +++++++
 xen/arch/arm/include/asm/arm64/hsr.h  |  1 +
 xen/arch/arm/include/asm/cpufeature.h | 14 ++++++------
 4 files changed, 46 insertions(+), 8 deletions(-)

diff --git a/xen/arch/arm/arm64/vsysreg.c b/xen/arch/arm/arm64/vsysreg.c
index d14258290f..520faa02ca 100644
--- a/xen/arch/arm/arm64/vsysreg.c
+++ b/xen/arch/arm/arm64/vsysreg.c
@@ -229,6 +229,7 @@ void do_sysreg(struct cpu_user_regs *regs,
      */
     case HSR_SYSREG_PMINTENSET_EL1:
     case HSR_SYSREG_PMINTENCLR_EL1:
+    case HSR_SYSREG_PMMIR_EL1:
         /*
          * Accessible from EL1 only, but if EL0 trap happens handle as
          * undef.
@@ -306,7 +307,6 @@ void do_sysreg(struct cpu_user_regs *regs,
     GENERATE_TID3_INFO(ID_PFR0_EL1, pfr32, 0)
     GENERATE_TID3_INFO(ID_PFR1_EL1, pfr32, 1)
     GENERATE_TID3_INFO(ID_PFR2_EL1, pfr32, 2)
-    GENERATE_TID3_INFO(ID_DFR0_EL1, dbg32, 0)
     GENERATE_TID3_INFO(ID_DFR1_EL1, dbg32, 1)
     GENERATE_TID3_INFO(ID_AFR0_EL1, aux32, 0)
     GENERATE_TID3_INFO(ID_MMFR0_EL1, mm32, 0)
@@ -326,6 +326,18 @@ void do_sysreg(struct cpu_user_regs *regs,
     GENERATE_TID3_INFO(MVFR1_EL1, mvfr, 1)
     GENERATE_TID3_INFO(MVFR2_EL1, mvfr, 2)
 
+    case HSR_SYSREG_ID_DFR0_EL1:
+    {
+        struct domain *d = current->domain;
+        union cpuinfo_dbg32 info_dbg32 = domain_cpuinfo.dbg32;
+
+        if ( !(d->options & XEN_DOMCTL_CDF_vpmu) )
+            info_dbg32.perfmon = 0;
+
+        return handle_ro_read_val(regs, regidx, hsr.sysreg.read, hsr, 1,
+                                  info_dbg32.bits[0]);
+    }
+
     case HSR_SYSREG_ID_AA64PFR0_EL1:
     {
         register_t guest_reg_value = domain_cpuinfo.pfr64.bits[0];
@@ -348,7 +360,6 @@ void do_sysreg(struct cpu_user_regs *regs,
     }
 
     GENERATE_TID3_INFO(ID_AA64PFR1_EL1, pfr64, 1)
-    GENERATE_TID3_INFO(ID_AA64DFR0_EL1, dbg64, 0)
     GENERATE_TID3_INFO(ID_AA64DFR1_EL1, dbg64, 1)
     GENERATE_TID3_INFO(ID_AA64ISAR0_EL1, isa64, 0)
     GENERATE_TID3_INFO(ID_AA64ISAR1_EL1, isa64, 1)
@@ -358,6 +369,22 @@ void do_sysreg(struct cpu_user_regs *regs,
     GENERATE_TID3_INFO(ID_AA64AFR0_EL1, aux64, 0)
     GENERATE_TID3_INFO(ID_AA64AFR1_EL1, aux64, 1)
 
+    case HSR_SYSREG_ID_AA64DFR0_EL1:
+    {
+        struct domain *d = current->domain;
+        union cpuinfo_dbg64 info_dbg64 = domain_cpuinfo.dbg64;
+
+        if ( !(d->options & XEN_DOMCTL_CDF_vpmu) )
+        {
+            info_dbg64.pmu_ver = 0;
+            info_dbg64.mtpmu = 0;
+            info_dbg64.pmss = 0;
+        }
+
+        return handle_ro_read_val(regs, regidx, hsr.sysreg.read, hsr, 1,
+                                  info_dbg64.bits[0]);
+    }
+
     case HSR_SYSREG_ID_AA64ZFR0_EL1:
     {
         /*
diff --git a/xen/arch/arm/cpufeature.c b/xen/arch/arm/cpufeature.c
index 94d14fb6a9..0e9bf15ca5 100644
--- a/xen/arch/arm/cpufeature.c
+++ b/xen/arch/arm/cpufeature.c
@@ -219,6 +219,14 @@ static int __init create_domain_cpuinfo(void)
     domain_cpuinfo.isa64.api = 0;
     domain_cpuinfo.isa64.gpa = 0;
     domain_cpuinfo.isa64.gpi = 0;
+
+    /* Hide SPE, TRBE, BRBE, and Trace Extensions */
+    domain_cpuinfo.dbg64.pms_ver = 0;
+    domain_cpuinfo.dbg64.trace_ver = 0;
+    domain_cpuinfo.dbg64.trace_filt = 0;
+    domain_cpuinfo.dbg64.trace_buffer = 0;
+    domain_cpuinfo.dbg64.ext_trc_buff = 0;
+    domain_cpuinfo.dbg64.brbe = 0;
 #endif
 
     /* Hide AMU support */
diff --git a/xen/arch/arm/include/asm/arm64/hsr.h 
b/xen/arch/arm/include/asm/arm64/hsr.h
index 1495ccddea..ed18184cc7 100644
--- a/xen/arch/arm/include/asm/arm64/hsr.h
+++ b/xen/arch/arm/include/asm/arm64/hsr.h
@@ -84,6 +84,7 @@
 #define HSR_SYSREG_FAR_EL1        HSR_SYSREG(3,0,c6, c0,0)
 #define HSR_SYSREG_PMINTENSET_EL1 HSR_SYSREG(3,0,c9,c14,1)
 #define HSR_SYSREG_PMINTENCLR_EL1 HSR_SYSREG(3,0,c9,c14,2)
+#define HSR_SYSREG_PMMIR_EL1      HSR_SYSREG(3,0,c9,c14,6)
 #define HSR_SYSREG_MAIR_EL1       HSR_SYSREG(3,0,c10,c2,0)
 #define HSR_SYSREG_AMAIR_EL1      HSR_SYSREG(3,0,c10,c3,0)
 #define HSR_SYSREG_ICC_SGI1R_EL1  HSR_SYSREG(3,0,c12,c11,5)
diff --git a/xen/arch/arm/include/asm/cpufeature.h 
b/xen/arch/arm/include/asm/cpufeature.h
index bf902a3970..ce8b58458f 100644
--- a/xen/arch/arm/include/asm/cpufeature.h
+++ b/xen/arch/arm/include/asm/cpufeature.h
@@ -208,7 +208,7 @@ struct cpuinfo_arm {
         };
     } pfr64;
 
-    union {
+    union cpuinfo_dbg64 {
         register_t bits[2];
         struct {
             /* DFR0 */
@@ -216,16 +216,18 @@ struct cpuinfo_arm {
             unsigned long trace_ver:4;
             unsigned long pmu_ver:4;
             unsigned long brps:4;
-            unsigned long __res0:4;
+            unsigned long pmss:4;
             unsigned long wrps:4;
-            unsigned long __res1:4;
+            unsigned long sebep:4;
             unsigned long ctx_cmps:4;
             unsigned long pms_ver:4;
             unsigned long double_lock:4;
             unsigned long trace_filt:4;
-            unsigned long __res2:4;
+            unsigned long trace_buffer:4;
             unsigned long mtpmu:4;
-            unsigned long __res3:12;
+            unsigned long brbe:4;
+            unsigned long ext_trc_buff:4;
+            unsigned long hpmn0:4;
 
             /* DFR1 */
             unsigned long __res4:64;
@@ -408,7 +410,7 @@ struct cpuinfo_arm {
         };
     } pfr32;
 
-    union {
+    union cpuinfo_dbg32 {
         register_t bits[2];
         struct {
             /* DFR0 */
-- 
2.43.0