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

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Message-Id: <DA5YWWPPVCQW.22VHONAQHOCHE@ventanamicro.com>
Date: Mon, 26 May 2025 11:00:30 +0200
From: Radim Krčmář <rkrcmar@...tanamicro.com>
To: "Atish Patra" <atish.patra@...ux.dev>, "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

2025-05-23T10:16:11-07:00, Atish Patra <atish.patra@...ux.dev>:
> 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.

Yes, I am all in favor of letting userspace provide all values in the
BASE extension.