[PATCH] xen/arm: don't read aarch32 regs when aarch32 isn't available

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

Don't read aarch32 system registers at boot time when the aarch32 state
is not available. They are UNKNOWN, so it is not useful to read them.
Moreover, on Cavium ThunderX reading ID_PFR2_EL1 causes a Xen crash.
Instead, only read them when aarch32 is available.

Leave the corresponding fields in struct cpuinfo_arm so that they
are read-as-zero from a guest.

Since we are editing identify_cpu, also fix the indentation: 4 spaces
instead of 8.

Fixes: 9cfdb489af81 ("xen/arm: Add ID registers and complete cpuinfo")
Link: https://marc.info/?l=xen-devel&m=161035501118086
Link: 
http://logs.test-lab.xenproject.org/osstest/logs/158293/test-arm64-arm64-xl-xsm/info.html
Suggested-by: Julien Grall <julien@xxxxxxx>
Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
---
 xen/arch/arm/cpufeature.c | 35 +++++++++++++++++++++--------------
 1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/xen/arch/arm/cpufeature.c b/xen/arch/arm/cpufeature.c
index 698bfa0201..b1c82ade49 100644
--- a/xen/arch/arm/cpufeature.c
+++ b/xen/arch/arm/cpufeature.c
@@ -101,29 +101,35 @@ int enable_nonboot_cpu_caps(const struct 
arm_cpu_capabilities *caps)
 
 void identify_cpu(struct cpuinfo_arm *c)
 {
-        c->midr.bits = READ_SYSREG(MIDR_EL1);
-        c->mpidr.bits = READ_SYSREG(MPIDR_EL1);
+    bool aarch32 = true;
+
+    c->midr.bits = READ_SYSREG(MIDR_EL1);
+    c->mpidr.bits = READ_SYSREG(MPIDR_EL1);
 
 #ifdef CONFIG_ARM_64
-        c->pfr64.bits[0] = READ_SYSREG(ID_AA64PFR0_EL1);
-        c->pfr64.bits[1] = READ_SYSREG(ID_AA64PFR1_EL1);
+    c->pfr64.bits[0] = READ_SYSREG(ID_AA64PFR0_EL1);
+    c->pfr64.bits[1] = READ_SYSREG(ID_AA64PFR1_EL1);
+
+    c->dbg64.bits[0] = READ_SYSREG(ID_AA64DFR0_EL1);
+    c->dbg64.bits[1] = READ_SYSREG(ID_AA64DFR1_EL1);
 
-        c->dbg64.bits[0] = READ_SYSREG(ID_AA64DFR0_EL1);
-        c->dbg64.bits[1] = READ_SYSREG(ID_AA64DFR1_EL1);
+    c->aux64.bits[0] = READ_SYSREG(ID_AA64AFR0_EL1);
+    c->aux64.bits[1] = READ_SYSREG(ID_AA64AFR1_EL1);
 
-        c->aux64.bits[0] = READ_SYSREG(ID_AA64AFR0_EL1);
-        c->aux64.bits[1] = READ_SYSREG(ID_AA64AFR1_EL1);
+    c->mm64.bits[0]  = READ_SYSREG(ID_AA64MMFR0_EL1);
+    c->mm64.bits[1]  = READ_SYSREG(ID_AA64MMFR1_EL1);
+    c->mm64.bits[2]  = READ_SYSREG(ID_AA64MMFR2_EL1);
 
-        c->mm64.bits[0]  = READ_SYSREG(ID_AA64MMFR0_EL1);
-        c->mm64.bits[1]  = READ_SYSREG(ID_AA64MMFR1_EL1);
-        c->mm64.bits[2]  = READ_SYSREG(ID_AA64MMFR2_EL1);
+    c->isa64.bits[0] = READ_SYSREG(ID_AA64ISAR0_EL1);
+    c->isa64.bits[1] = READ_SYSREG(ID_AA64ISAR1_EL1);
 
-        c->isa64.bits[0] = READ_SYSREG(ID_AA64ISAR0_EL1);
-        c->isa64.bits[1] = READ_SYSREG(ID_AA64ISAR1_EL1);
+    c->zfr64.bits[0] = READ_SYSREG(ID_AA64ZFR0_EL1);
 
-        c->zfr64.bits[0] = READ_SYSREG(ID_AA64ZFR0_EL1);
+    aarch32 = c->pfr64.el1 == 2;
 #endif
 
+    if ( aarch32 )
+    {
         c->pfr32.bits[0] = READ_SYSREG(ID_PFR0_EL1);
         c->pfr32.bits[1] = READ_SYSREG(ID_PFR1_EL1);
         c->pfr32.bits[2] = READ_SYSREG(ID_PFR2_EL1);
@@ -153,6 +159,7 @@ void identify_cpu(struct cpuinfo_arm *c)
 #ifndef MVFR2_MAYBE_UNDEFINED
         c->mvfr.bits[2] = READ_SYSREG(MVFR2_EL1);
 #endif
+    }
 }
 
 /*
-- 
2.17.1