From: "Daniel P. Berrangé" <berrange@redhat.com>
To: Daniel Henrique Barboza <dbarboza@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 2/2] target/riscv/tcg-cpu.c: add extension properties for all cpus
Date: Fri, 29 Sep 2023 11:38:01 +0100 [thread overview]
Message-ID: <ZRapCe9kGyw52bLS@redhat.com> (raw)
In-Reply-To: <20230926183109.165878-3-dbarboza@ventanamicro.com>
On Tue, Sep 26, 2023 at 03:31:09PM -0300, Daniel Henrique Barboza wrote:
> At this moment we do not expose extension properties for vendor CPUs
> because that would allow users to change them via command line. The
> drawback is that if we were to add an API that shows all CPU properties,
> e.g. qmp-query-cpu-model-expansion, we won't be able to show extensions
> state of vendor CPUs.
>
> We have the required machinery to create extension properties for vendor
> CPUs while not allowing users to enable extensions. Disabling existing
> extensions is allowed since it can be useful for debugging.
>
> Change the set() callback cpu_set_multi_ext_cfg() to allow enabling
> extensions only for generic CPUs. In cpu_add_multi_ext_prop() let's not
> set the default values for the properties if we're not dealing with
> generic CPUs, otherwise the values set in cpu_init() of vendor CPUs will
> be overwritten. And finally, in tcg_cpu_instance_init(), add cpu user
> properties for all CPUs.
>
> For the veyron-v1 CPU, we're now able to disable existing extensions
> like smstateen:
>
> $ ./build/qemu-system-riscv64 --nographic -M virt \
> -cpu veyron-v1,smstateen=false
>
> But setting extensions that the CPU didn't set during cpu_init(), like
> V, is not allowed:
>
> $ ./build/qemu-system-riscv64 --nographic -M virt \
> -cpu veyron-v1,v=true
> qemu-system-riscv64: can't apply global veyron-v1-riscv-cpu.v=true:
> 'veyron-v1' CPU does not allow enabling extensions
Why should we block the user if they want to enable an extra
feature, over and above what is built-in to the CPU model ?
Is there some technical reason that prevents this from working ?
With regards,
Daniel
--
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next prev parent reply other threads:[~2023-09-29 10:38 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-26 18:31 [PATCH 0/2] riscv: add extension properties for all cpus Daniel Henrique Barboza
2023-09-26 18:31 ` [PATCH 1/2] target/riscv: add riscv_cpu_get_name() Daniel Henrique Barboza
2023-09-27 4:58 ` Alistair Francis
2023-09-26 18:31 ` [PATCH 2/2] target/riscv/tcg-cpu.c: add extension properties for all cpus Daniel Henrique Barboza
2023-09-29 5:13 ` Alistair Francis
2023-09-29 10:38 ` Daniel P. Berrangé [this message]
2023-10-09 2:37 ` Alistair Francis
2023-09-29 5:29 ` [PATCH 0/2] riscv: " Alistair Francis
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