linux-kernel - Re: [PATCH v3 9/9] RISC-V: KVM: Upgrade the supported SBI version to 3.0

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Message-ID: <61627296-6f94-45ea-9410-ed0ea2251870@linux.dev>
Date: Fri, 23 May 2025 10:16:11 -0700
From: Atish Patra <atish.patra@...ux.dev>
To: Radim Krčmář <rkrcmar@...tanamicro.com>,
 Anup Patel <anup@...infault.org>, Will Deacon <will@...nel.org>,
 Mark Rutland <mark.rutland@....com>, Paul Walmsley
 <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>,
 Mayuresh Chitale <mchitale@...tanamicro.com>
Cc: linux-riscv@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org, Palmer Dabbelt <palmer@...osinc.com>,
 kvm@...r.kernel.org, kvm-riscv@...ts.infradead.org,
 linux-riscv <linux-riscv-bounces@...ts.infradead.org>
Subject: Re: [PATCH v3 9/9] RISC-V: KVM: Upgrade the supported SBI version to
 3.0


On 5/23/25 6:31 AM, Radim Krčmář wrote:
> 2025-05-22T12:03:43-07:00, Atish Patra <atishp@...osinc.com>:
>> Upgrade the SBI version to v3.0 so that corresponding features
>> can be enabled in the guest.
>>
>> Signed-off-by: Atish Patra <atishp@...osinc.com>
>> ---
>> diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/include/asm/kvm_vcpu_sbi.h
>> -#define KVM_SBI_VERSION_MAJOR 2
>> +#define KVM_SBI_VERSION_MAJOR 3
> I think it's time to add versioning to KVM SBI implementation.
> Userspace should be able to select the desired SBI version and KVM would
> tell the guest that newer features are not supported.

We can achieve that through onereg interface by disabling individual SBI 
extensions.
We can extend the existing onereg interface to disable a specific SBI 
version directly
instead of individual ones to save those IOCTL as well.

> We could somewhat get away with the userspace_sbi patch I posted,
> because userspace would at least be in control of the SBI version, but
> it would still be incorrect without a KVM enforcement, because a
> misbehaving guest could use features that should not be supported.