linux-kernel - Re: [PATCH v8 13/14] RISC-V: KVM: add support for FWFT SBI extension

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Message-ID: <9f9e2869-725d-4590-887a-9b0ef091472e@rivosinc.com>
Date: Fri, 23 May 2025 17:29:49 +0200
From: Clément Léger <cleger@...osinc.com>
To: Radim Krčmář <rkrcmar@...tanamicro.com>,
 Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
 <palmer@...belt.com>, Anup Patel <anup@...infault.org>,
 Atish Patra <atishp@...shpatra.org>, Shuah Khan <shuah@...nel.org>,
 Jonathan Corbet <corbet@....net>, linux-riscv@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
 kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org,
 linux-kselftest@...r.kernel.org
Cc: Samuel Holland <samuel.holland@...ive.com>,
 Andrew Jones <ajones@...tanamicro.com>, Deepak Gupta <debug@...osinc.com>,
 Charlie Jenkins <charlie@...osinc.com>, Atish Patra <atishp@...osinc.com>,
 linux-riscv <linux-riscv-bounces@...ts.infradead.org>
Subject: Re: [PATCH v8 13/14] RISC-V: KVM: add support for FWFT SBI extension



On 23/05/2025 15:05, Radim Krčmář wrote:
> 2025-05-23T12:19:30+02:00, Clément Léger <cleger@...osinc.com>:
>> +++ b/arch/riscv/kvm/vcpu_sbi_fwft.c
>> +static const enum sbi_fwft_feature_t kvm_fwft_defined_features[] = {
>> +	SBI_FWFT_MISALIGNED_EXC_DELEG,
>> +	SBI_FWFT_LANDING_PAD,
>> +	SBI_FWFT_SHADOW_STACK,
>> +	SBI_FWFT_DOUBLE_TRAP,
>> +	SBI_FWFT_PTE_AD_HW_UPDATING,
>> +	SBI_FWFT_POINTER_MASKING_PMLEN,
>> +};
> 
> How will userspace control which subset of these features is allowed in
> the guest?
> 
> (We can reuse the KVM SBI extension interface if we don't want to add a
>  FWFT specific ONE_REG.)

Hi Radim,

I didn't looked at that part. But most likely using the kvm one reg
interface seems ok like what is done for STA ? We could have per feature
override with one reg per feature.

Is this something blocking though ? We'd like to merge FWFT once SBI 3.0
is ratified so that would be nice not delaying it too much. I'll take a
look at it to see if it isn't too long to implement.

Thanks,

Clément

> 
> Thanks.