[PATCH v2 18/18] target/riscv/kvm.c: read/write (cbom|cboz)_blocksize in KVM

[Daniel Henrique Barboza <dbarboza@ventanamicro.com>]

If we don't set a proper cbom_blocksize|cboz_blocksize in the FDT the
Linux Kernel will fail to detect the availability of the CBOM/CBOZ
extensions, regardless of the contents of the 'riscv,isa' DT prop.

The FDT is being written using the cpu->cfg.cbom|z_blocksize attributes,
so let's expose them as user properties like it is already done with
TCG.

This will also require us to determine proper blocksize values during
init() time since the FDT is already created during realize(). We'll
take a ride in kvm_riscv_init_multiext_cfg() to do it. Note that we
don't need to fetch both cbom and cboz blocksizes every time: check for
their parent extensions (icbom and icboz) and only read the blocksizes
if needed.

In contrast with cbom/z_blocksize properties from TCG, the user is not
able to set any value that is different from the 'host' value when
running KVM. KVM can be particularly harsh dealing with it: a ENOTSUPP
can be thrown for the mere attempt of executing kvm_set_one_reg() for
these 2 regs.

Hopefully, we don't need to call kvm_set_one_reg() for these regs.
We'll check if the user input matches the host value in
kvm_cpu_set_cbomz_blksize(), the set() accessor for both blocksize
properties. We'll fail fast since it's already known to not be
supported.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
---
 target/riscv/kvm.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 70 insertions(+)

diff --git a/target/riscv/kvm.c b/target/riscv/kvm.c
index 3a9f7b0722..ccd2375d8d 100644
--- a/target/riscv/kvm.c
+++ b/target/riscv/kvm.c
@@ -283,6 +283,42 @@ static void kvm_cpu_set_multi_ext_cfg(Object *obj, Visitor *v,
     kvm_cpu_cfg_set(cpu, multi_ext_cfg, value);
 }
 
+static KVMCPUConfig kvm_cbom_blocksize = {
+    .name = "cbom_blocksize",
+    .offset = CPUCFG(cbom_blocksize),
+    .kvm_reg_id = KVM_REG_RISCV_CONFIG_REG(zicbom_block_size)
+};
+
+static KVMCPUConfig kvm_cboz_blocksize = {
+    .name = "cboz_blocksize",
+    .offset = CPUCFG(cboz_blocksize),
+    .kvm_reg_id = KVM_REG_RISCV_CONFIG_REG(zicboz_block_size)
+};
+
+static void kvm_cpu_set_cbomz_blksize(Object *obj, Visitor *v,
+                                      const char *name,
+                                      void *opaque, Error **errp)
+{
+    KVMCPUConfig *cbomz_cfg = opaque;
+    RISCVCPU *cpu = RISCV_CPU(obj);
+    uint16_t value, *host_val;
+
+    if (!visit_type_uint16(v, name, &value, errp)) {
+        return;
+    }
+
+    host_val = kvmconfig_get_cfg_addr(cpu, cbomz_cfg);
+
+    if (value != *host_val) {
+        error_report("Unable to set %s to a different value than "
+                     "the host (%u)",
+                     cbomz_cfg->name, *host_val);
+        exit(EXIT_FAILURE);
+    }
+
+    cbomz_cfg->user_set = true;
+}
+
 static void kvm_riscv_update_cpu_cfg_isa_ext(RISCVCPU *cpu, CPUState *cs)
 {
     CPURISCVState *env = &cpu->env;
@@ -332,6 +368,14 @@ static void kvm_riscv_add_cpu_user_properties(Object *cpu_obj)
                             kvm_cpu_set_multi_ext_cfg,
                             NULL, multi_cfg);
     }
+
+    object_property_add(cpu_obj, "cbom_blocksize", "uint16",
+                        NULL, kvm_cpu_set_cbomz_blksize,
+                        NULL, &kvm_cbom_blocksize);
+
+    object_property_add(cpu_obj, "cboz_blocksize", "uint16",
+                        NULL, kvm_cpu_set_cbomz_blksize,
+                        NULL, &kvm_cboz_blocksize);
 }
 
 static int kvm_riscv_get_regs_core(CPUState *cs)
@@ -647,6 +691,24 @@ static void kvm_riscv_init_misa_ext_mask(RISCVCPU *cpu,
     env->misa_ext = env->misa_ext_mask;
 }
 
+static void kvm_riscv_read_cbomz_blksize(RISCVCPU *cpu, KVMScratchCPU *kvmcpu,
+                                         KVMCPUConfig *cbomz_cfg)
+{
+    CPURISCVState *env = &cpu->env;
+    struct kvm_one_reg reg;
+    int ret;
+
+    reg.id = kvm_riscv_reg_id(env, KVM_REG_RISCV_CONFIG,
+                              cbomz_cfg->kvm_reg_id);
+    reg.addr = (uint64_t)kvmconfig_get_cfg_addr(cpu, cbomz_cfg);
+    ret = ioctl(kvmcpu->cpufd, KVM_GET_ONE_REG, &reg);
+    if (ret != 0) {
+        error_report("Unable to read KVM reg %s, error %d",
+                     cbomz_cfg->name, ret);
+        exit(EXIT_FAILURE);
+    }
+}
+
 static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
 {
     CPURISCVState *env = &cpu->env;
@@ -678,6 +740,14 @@ static void kvm_riscv_init_multiext_cfg(RISCVCPU *cpu, KVMScratchCPU *kvmcpu)
 
         kvm_cpu_cfg_set(cpu, multi_ext_cfg, val);
     }
+
+    if (cpu->cfg.ext_icbom) {
+        kvm_riscv_read_cbomz_blksize(cpu, kvmcpu, &kvm_cbom_blocksize);
+    }
+
+    if (cpu->cfg.ext_icboz) {
+        kvm_riscv_read_cbomz_blksize(cpu, kvmcpu, &kvm_cboz_blocksize);
+    }
 }
 
 void kvm_riscv_init_user_properties(Object *cpu_obj)
-- 
2.40.1