target/arm: Set KVM_ARM_VCPU_SVE while probing the host

Because we weren't setting this flag, our probe of ID_AA64ZFR0
was always returning zero.  This also obviates the adjustment
of ID_AA64PFR0, which had sanitized the SVE field.

The effects of the bug are not visible, because the only thing that
ID_AA64ZFR0 is used for within qemu at present is tcg translation.
The other tests for SVE within KVM are via ID_AA64PFR0.SVE.

Reported-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220726045828.53697-3-richard.henderson@linaro.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 13 insertions, 14 deletions

diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
index bb1516b..43cd7eb 100644
--- a/target/arm/kvm64.c
+++ b/target/arm/kvm64.c
@@ -507,7 +507,6 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
     bool sve_supported;
     bool pmu_supported = false;
     uint64_t features = 0;
-    uint64_t t;
     int err;
 
     /* Old kernels may not know about the PREFERRED_TARGET ioctl: however
@@ -528,10 +527,17 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
     struct kvm_vcpu_init init = { .target = -1, };
 
     /*
-     * Ask for Pointer Authentication if supported. We can't play the
-     * SVE trick of synthesising the ID reg as KVM won't tell us
-     * whether we have the architected or IMPDEF version of PAuth, so
-     * we have to use the actual ID regs.
+     * Ask for SVE if supported, so that we can query ID_AA64ZFR0,
+     * which is otherwise RAZ.
+     */
+    sve_supported = kvm_arm_sve_supported();
+    if (sve_supported) {
+        init.features[0] |= 1 << KVM_ARM_VCPU_SVE;
+    }
+
+    /*
+     * Ask for Pointer Authentication if supported, so that we get
+     * the unsanitized field values for AA64ISAR1_EL1.
      */
     if (kvm_arm_pauth_supported()) {
         init.features[0] |= (1 << KVM_ARM_VCPU_PTRAUTH_ADDRESS |
@@ -675,20 +681,13 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
         }
     }
 
-    sve_supported = kvm_arm_sve_supported();
-
-    /* Add feature bits that can't appear until after VCPU init. */
     if (sve_supported) {
-        t = ahcf->isar.id_aa64pfr0;
-        t = FIELD_DP64(t, ID_AA64PFR0, SVE, 1);
-        ahcf->isar.id_aa64pfr0 = t;
-
         /*
          * There is a range of kernels between kernel commit 73433762fcae
          * and f81cb2c3ad41 which have a bug where the kernel doesn't expose
          * SYS_ID_AA64ZFR0_EL1 via the ONE_REG API unless the VM has enabled
-         * SVE support, so we only read it here, rather than together with all
-         * the other ID registers earlier.
+         * SVE support, which resulted in an error rather than RAZ.
+         * So only read the register if we set KVM_ARM_VCPU_SVE above.
          */
         err |= read_sys_reg64(fdarray[2], &ahcf->isar.id_aa64zfr0,
                               ARM64_SYS_REG(3, 0, 0, 4, 4));