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

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Message-Id: <DA3KSSN3MJW5.2CM40VEWBWDHQ@ventanamicro.com>
Date: Fri, 23 May 2025 15:31:32 +0200
From: Radim Krčmář <rkrcmar@...tanamicro.com>
To: "Atish Patra" <atishp@...osinc.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

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 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.