Re: [PATCH 02/16] hw/riscv/virt.c: skip 'mmu-type' FDT if satp mode not set

From: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
To: Andrew Jones <ajones@ventanamicro.com>
Cc: qemu-devel@nongnu.org, qemu-riscv@nongnu.org,
	alistair.francis@wdc.com, bmeng@tinylab.org,
	liweiwei@iscas.ac.cn, zhiwei_liu@linux.alibaba.com,
	palmer@rivosinc.com
Subject: Re: [PATCH 02/16] hw/riscv/virt.c: skip 'mmu-type' FDT if satp mode not set
Date: Tue, 6 Jun 2023 17:07:03 -0300	[thread overview]
Message-ID: <34b3ad50-7b36-99c3-134f-0a1897e7cffe@ventanamicro.com> (raw)
In-Reply-To: <20230606-523ed1960aaa8070f5639237@orel>

On 6/6/23 10:13, Andrew Jones wrote:
> On Tue, May 30, 2023 at 04:46:09PM -0300, Daniel Henrique Barboza wrote:
>> The absence of a satp mode in riscv_host_cpu_init() is causing the
>> following error:
>>
>> $ sudo ./qemu/build/qemu-system-riscv64  -machine virt,accel=kvm \
>>      -m 2G -smp 1  -nographic -snapshot \
>>      -kernel ./guest_imgs/Image \
>>      -initrd ./guest_imgs/rootfs_kvm_riscv64.img \
>>      -append "earlycon=sbi root=/dev/ram rw" \
>>      -cpu host
>> **
>> ERROR:../target/riscv/cpu.c:320:satp_mode_str: code should not be
>> reached
>> Bail out! ERROR:../target/riscv/cpu.c:320:satp_mode_str: code should
>> not be reached
>> Aborted
>>
>> The error is triggered from create_fdt_socket_cpus() in hw/riscv/virt.c.
>> It's trying to get satp_mode_str for a NULL cpu->cfg.satp_mode.map.
>>
>> For this KVM 'cpu' we would need to inherit the satp supported modes
>> from the RISC-V host. At this moment this is not possible because the
>> KVM driver does not support it. And even when it does we can't just let
>> this broken for every other older kernel.
>>
>> Skip the 'mmu-type' FDT node if there's no satp_mode set.
> 
> This seems reasonable, since mmu-type is not a required node, according to
> [1], and there's nothing we can put in it, which would be correct, until
> we can get the information from KVM.
> 
> [1] https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/cpu.yaml
> 
>>
>> Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
>> ---
>>   hw/riscv/virt.c | 14 +++++++-------
>>   1 file changed, 7 insertions(+), 7 deletions(-)
>>
>> diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
>> index 4e3efbee16..8aa907e81f 100644
>> --- a/hw/riscv/virt.c
>> +++ b/hw/riscv/virt.c
>> @@ -243,13 +243,13 @@ static void create_fdt_socket_cpus(RISCVVirtState *s, int socket,
>>               s->soc[socket].hartid_base + cpu);
>>           qemu_fdt_add_subnode(ms->fdt, cpu_name);
>>   
>> -        satp_mode_max = satp_mode_max_from_map(
>> -            s->soc[socket].harts[cpu].cfg.satp_mode.map);
>> -        sv_name = g_strdup_printf("riscv,%s",
>> -                                  satp_mode_str(satp_mode_max, is_32_bit));
>> -        qemu_fdt_setprop_string(ms->fdt, cpu_name, "mmu-type", sv_name);
>> -        g_free(sv_name);
>> -
>> +        if (cpu_ptr->cfg.satp_mode.supported != 0) {
>> +            satp_mode_max = satp_mode_max_from_map(cpu_ptr->cfg.satp_mode.map);
>> +            sv_name = g_strdup_printf("riscv,%s",
>> +                                      satp_mode_str(satp_mode_max, is_32_bit));
>> +            qemu_fdt_setprop_string(ms->fdt, cpu_name, "mmu-type", sv_name);
>> +            g_free(sv_name);
>> +        }
>>   
>>           name = riscv_isa_string(cpu_ptr);
>>           qemu_fdt_setprop_string(ms->fdt, cpu_name, "riscv,isa", name);
>> -- 
>> 2.40.1
>>
>>
> 
> Adding a sentence, like what I wrote above, to the commit message in order
> to provide better justification might be nice, but either way
> 
> Reviewed-by: Andrew Jones <ajones@ventanamicro.com>

Thanks! Commit message amended for v2 as follows:

(....)

Since mmu-type is not a required node, according to [1], skip the
'mmu-type' FDT node if there's no satp_mode set. We'll revisit this
logic when we can get satp information from KVM.

[1] https://github.com/devicetree-org/dt-schema/blob/main/dtschema/schemas/cpu.yaml

Daniel

> 
> Thanks,
> drew