Now we have isar_feature test functions that look at fields in the
ID_AA64DFR0_EL1 and ID_DFR0 ID registers, add the code that reads
these register values from KVM so that the checks behave correctly
when we're using KVM.

No isar_feature function tests ID_AA64DFR1_EL1 or DBGDIDR yet, but we
add it to maintain the invariant that every field in the
ARMISARegisters struct is populated for a KVM CPU and can be relied
on.  This requirement isn't actually written down yet, so add a note
to the relevant comment.

Signed-off-by: Peter Maydell <peter.mayd...@linaro.org>
---
 target/arm/cpu.h   |  5 +++++
 target/arm/kvm32.c |  8 ++++++++
 target/arm/kvm64.c | 36 ++++++++++++++++++++++++++++++++++++
 3 files changed, 49 insertions(+)

diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index 3c996db3e45..e043932fcb1 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -853,6 +853,11 @@ struct ARMCPU {
      * prefix means a constant register.
      * Some of these registers are split out into a substructure that
      * is shared with the translators to control the ISA.
+     *
+     * Note that if you add an ID register to the ARMISARegisters struct
+     * you need to also update the 32-bit and 64-bit versions of the
+     * kvm_arm_get_host_cpu_features() function to correctly populate the
+     * field by reading the value from the KVM vCPU.
      */
     struct ARMISARegisters {
         uint32_t id_isar0;
diff --git a/target/arm/kvm32.c b/target/arm/kvm32.c
index 3a8b437eef0..bca02553b25 100644
--- a/target/arm/kvm32.c
+++ b/target/arm/kvm32.c
@@ -97,6 +97,9 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
         ahcf->isar.id_isar6 = 0;
     }
 
+    err |= read_sys_reg32(fdarray[2], &ahcf->isar.id_dfr0,
+                          ARM_CP15_REG32(0, 0, 1, 2));
+
     err |= read_sys_reg32(fdarray[2], &ahcf->isar.mvfr0,
                           KVM_REG_ARM | KVM_REG_SIZE_U32 |
                           KVM_REG_ARM_VFP | KVM_REG_ARM_VFP_MVFR0);
@@ -108,6 +111,11 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures 
*ahcf)
      * Fortunately there is not yet anything in there that affects migration.
      */
 
+    /*
+     * There is no way to read DBGDIDR, because currently 32-bit KVM
+     * doesn't implement debug at all. Leave it at zero.
+     */
+
     kvm_arm_destroy_scratch_host_vcpu(fdarray);
 
     if (err < 0) {
diff --git a/target/arm/kvm64.c b/target/arm/kvm64.c
index 3bae9e4a663..527532f2b37 100644
--- a/target/arm/kvm64.c
+++ b/target/arm/kvm64.c
@@ -541,6 +541,10 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures 
*ahcf)
     } else {
         err |= read_sys_reg64(fdarray[2], &ahcf->isar.id_aa64pfr1,
                               ARM64_SYS_REG(3, 0, 0, 4, 1));
+        err |= read_sys_reg64(fdarray[2], &ahcf->isar.id_aa64dfr0,
+                              ARM64_SYS_REG(3, 0, 0, 5, 0));
+        err |= read_sys_reg64(fdarray[2], &ahcf->isar.id_aa64dfr1,
+                              ARM64_SYS_REG(3, 0, 0, 5, 1));
         err |= read_sys_reg64(fdarray[2], &ahcf->isar.id_aa64isar0,
                               ARM64_SYS_REG(3, 0, 0, 6, 0));
         err |= read_sys_reg64(fdarray[2], &ahcf->isar.id_aa64isar1,
@@ -559,6 +563,8 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures *ahcf)
          * than skipping the reads and leaving 0, as we must avoid
          * considering the values in every case.
          */
+        err |= read_sys_reg32(fdarray[2], &ahcf->isar.id_dfr0,
+                              ARM64_SYS_REG(3, 0, 0, 1, 2));
         err |= read_sys_reg32(fdarray[2], &ahcf->isar.id_isar0,
                               ARM64_SYS_REG(3, 0, 0, 2, 0));
         err |= read_sys_reg32(fdarray[2], &ahcf->isar.id_isar1,
@@ -580,6 +586,36 @@ bool kvm_arm_get_host_cpu_features(ARMHostCPUFeatures 
*ahcf)
                               ARM64_SYS_REG(3, 0, 0, 3, 1));
         err |= read_sys_reg32(fdarray[2], &ahcf->isar.mvfr2,
                               ARM64_SYS_REG(3, 0, 0, 3, 2));
+
+        /*
+         * DBGDIDR is a bit complicated because the kernel doesn't
+         * provide an accessor for it in 64-bit mode, which is what this
+         * scratch VM is in, and there's no architected "64-bit sysreg
+         * which reads the same as the 32-bit register" the way there is
+         * for other ID registers. Instead we synthesize a value from the
+         * AArch64 ID_AA64DFR0, the same way the kernel code in
+         * arch/arm64/kvm/sys_regs.c:trap_dbgidr() does.
+         * We only do this if the CPU supports AArch32 at EL1.
+         */
+        if (FIELD_EX32(ahcf->isar.id_aa64pfr0, ID_AA64PFR0, EL1) >= 2) {
+            int wrps = FIELD_EX64(ahcf->isar.id_aa64dfr0, ID_AA64DFR0, WRPS);
+            int brps = FIELD_EX64(ahcf->isar.id_aa64dfr0, ID_AA64DFR0, BRPS);
+            int ctx_cmps =
+                FIELD_EX64(ahcf->isar.id_aa64dfr0, ID_AA64DFR0, CTX_CMPS);
+            int version = 6; /* ARMv8 debug architecture */
+            bool has_el3 =
+                !!FIELD_EX32(ahcf->isar.id_aa64pfr0, ID_AA64PFR0, EL3);
+            uint32_t dbgdidr = 0;
+
+            dbgdidr = FIELD_DP32(dbgdidr, DBGDIDR, WRPS, wrps);
+            dbgdidr = FIELD_DP32(dbgdidr, DBGDIDR, BRPS, brps);
+            dbgdidr = FIELD_DP32(dbgdidr, DBGDIDR, CTX_CMPS, ctx_cmps);
+            dbgdidr = FIELD_DP32(dbgdidr, DBGDIDR, VERSION, version);
+            dbgdidr = FIELD_DP32(dbgdidr, DBGDIDR, NSUHD_IMP, has_el3);
+            dbgdidr = FIELD_DP32(dbgdidr, DBGDIDR, SE_IMP, has_el3);
+            dbgdidr |= (1 << 16); /* RES1 bit */
+            ahcf->isar.dbgdidr = dbgdidr;
+        }
     }
 
     sve_supported = ioctl(fdarray[0], KVM_CHECK_EXTENSION, KVM_CAP_ARM_SVE) > 
0;
-- 
2.20.1


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