[RFC PATCH 3/8] xen/arm: Expose SVE feature to the guest

[Luca Fancellu <luca.fancellu@xxxxxxx>]

When a guest is allowed to use SVE, expose the SVE features through
the identification registers.

Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
---
 xen/arch/arm/arm64/vsysreg.c | 39 ++++++++++++++++++++++++++++++++++--
 1 file changed, 37 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/arm64/vsysreg.c b/xen/arch/arm/arm64/vsysreg.c
index 758750983c11..10048bb4d221 100644
--- a/xen/arch/arm/arm64/vsysreg.c
+++ b/xen/arch/arm/arm64/vsysreg.c
@@ -18,6 +18,7 @@
 
 #include <xen/sched.h>
 
+#include <asm/arm64/cpufeature.h>
 #include <asm/current.h>
 #include <asm/regs.h>
 #include <asm/traps.h>
@@ -295,7 +296,28 @@ void do_sysreg(struct cpu_user_regs *regs,
     GENERATE_TID3_INFO(MVFR0_EL1, mvfr, 0)
     GENERATE_TID3_INFO(MVFR1_EL1, mvfr, 1)
     GENERATE_TID3_INFO(MVFR2_EL1, mvfr, 2)
-    GENERATE_TID3_INFO(ID_AA64PFR0_EL1, pfr64, 0)
+
+    case HSR_SYSREG_ID_AA64PFR0_EL1:
+    {
+        register_t guest_reg_value = guest_cpuinfo.pfr64.bits[0];
+
+        if ( is_sve_domain(v->domain) )
+        {
+            /* 4 is the SVE field width in id_aa64pfr0_el1 */
+            uint64_t mask = GENMASK(ID_AA64PFR0_SVE_SHIFT + 4 - 1,
+                                    ID_AA64PFR0_SVE_SHIFT);
+            /* sysval is the sve field on the system */
+            uint64_t sysval = cpuid_feature_extract_unsigned_field_width(
+                                system_cpuinfo.pfr64.bits[0],
+                                ID_AA64PFR0_SVE_SHIFT, 4);
+            guest_reg_value &= ~mask;
+            guest_reg_value |= (sysval << ID_AA64PFR0_SVE_SHIFT) & mask;
+        }
+
+        return handle_ro_read_val(regs, regidx, hsr.sysreg.read, hsr, 1,
+                                  guest_reg_value);
+    }
+
     GENERATE_TID3_INFO(ID_AA64PFR1_EL1, pfr64, 1)
     GENERATE_TID3_INFO(ID_AA64DFR0_EL1, dbg64, 0)
     GENERATE_TID3_INFO(ID_AA64DFR1_EL1, dbg64, 1)
@@ -306,7 +328,20 @@ void do_sysreg(struct cpu_user_regs *regs,
     GENERATE_TID3_INFO(ID_AA64MMFR2_EL1, mm64, 2)
     GENERATE_TID3_INFO(ID_AA64AFR0_EL1, aux64, 0)
     GENERATE_TID3_INFO(ID_AA64AFR1_EL1, aux64, 1)
-    GENERATE_TID3_INFO(ID_AA64ZFR0_EL1, zfr64, 0)
+
+    case HSR_SYSREG_ID_AA64ZFR0_EL1:
+    {
+        /*
+         * When the guest has the SVE feature enabled, the whole 
id_aa64zfr0_el1
+         * needs to be exposed.
+         */
+        register_t guest_reg_value = guest_cpuinfo.zfr64.bits[0];
+        if ( is_sve_domain(v->domain) )
+            guest_reg_value = system_cpuinfo.zfr64.bits[0];
+
+        return handle_ro_read_val(regs, regidx, hsr.sysreg.read, hsr, 1,
+                                  guest_reg_value);
+    }
 
     /*
      * Those cases are catching all Reserved registers trapped by TID3 which
-- 
2.17.1