Re: [PATCH] KVM: RISC-V: reset smstateen CSRs

["Radim Krčmář" <rkrcmar@ventanamicro.com>]

2025-03-25T22:27:41+05:30, Anup Patel <apatel@ventanamicro.com>:
> On Tue, Mar 25, 2025 at 8:58 PM Anup Patel <apatel@ventanamicro.com> wrote:
>>
>> On Tue, Mar 25, 2025 at 12:01 AM Radim Krčmář <rkrcmar@ventanamicro.com> wrote:
>> >
>> > Hi, I'm sending this early to ventana-sw as we hit the issue in today's
>> > slack discussion.  I only compile-tested it so far and it will take me a
>> > while to trigger a bug and verify the solution.
>> >
>> > ---8<--
>> > The smstateen CSRs control which stateful features are enabled in
>> > VU-mode.  SU-mode must properly context switch the state of all enabled
>> > features.
>> >
>> > Reset the smstateen CSRs, because SU-mode might not know that it must
>> > context switch the state.  Reset unconditionally as it is shorter and
>> > safer, and not that much slower.
>> >
>> > Fixes: 81f0f314fec9 ("RISCV: KVM: Add sstateen0 context save/restore")
>> > Cc: stable@vger.kernel.org
>> > Signed-off-by: Radim Krčmář <rkrcmar@ventanamicro.com>
>>
>> How about moving "struct kvm_vcpu_smstateen_csr smstateen" from
>> "struct kvm_vcpu_arch" to "struct kvm_vcpu_csr". This way we will not
>> need an extra "struct kvm_vcpu_smstateen_csr reset_smstateen_csr"
>> in "struct kvm_vcpu_csr".

It is tricky, because kvm_riscv_vcpu_general_set_csr calculates the
amount of registers accessible to userspace based the on size of
kvm_vcpu_csr.

We'd have to make changes to logic before expanding kvm_vcpu_csr with
kvm_vcpu_smstateen_csr.  At that point, I think it be much easier to
just put all csrs to kvm_vcpu_csr directly, which would also simplify
future extensions.

> Other than my comment, this looks good for upstreaming.

I think the current version is more appropriate for stable, and we can
implement your suggestion afterwards.

Thanks.