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Fri, 30 May 2025 04:09:44 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Fri, 30 May 2025 13:09:43 +0200 Message-Id: To: "Atish Patra" , "Andrew Jones" From: =?utf-8?q?Radim_Kr=C4=8Dm=C3=A1=C5=99?= Subject: Re: [PATCH v3 9/9] RISC-V: KVM: Upgrade the supported SBI version to 3.0 Cc: "Anup Patel" , "Will Deacon" , "Mark Rutland" , "Paul Walmsley" , "Palmer Dabbelt" , "Mayuresh Chitale" , , , , , , "linux-riscv" References: <20250522-pmu_event_info-v3-0-f7bba7fd9cfe@rivosinc.com> <20250522-pmu_event_info-v3-9-f7bba7fd9cfe@rivosinc.com> <61627296-6f94-45ea-9410-ed0ea2251870@linux.dev> <20250526-224478e15ee50987124a47ac@orel> <20250528-ff9f6120de39c3e4eefc5365@orel> <1169138f-8445-4522-94dd-ad008524c600@linux.dev> <2bac252c-883c-4f8a-9ae1-283660991520@linux.dev> In-Reply-To: <2bac252c-883c-4f8a-9ae1-283660991520@linux.dev> 2025-05-29T11:44:38-07:00, Atish Patra : > On 5/29/25 3:24 AM, Radim Kr=C4=8Dm=C3=A1=C5=99 wrote: >> I originally gave up on the idea, but I feel kinda bad for Drew now, so >> trying again: > > I am sorry if some of my replies came across in the wrong way. That was= =20 > never > the intention. I didn't mean to accuse you, my apologies. I agree with Drew's positions, so to expand on a question that wasn't touched in his mail: >> Even if userspace wants SBI for the M-mode interface, security minded > This is probably a 3rd one ? Why we want M-mode interface in the user=20 > space ? It is about turning KVM into an ISA accelerator. A guest thinks it is running in S/HS-mode. The ecall instruction traps to M-mode. RISC-V H extension doesn't accelerate M-mode, so we have to emulate the trap in software. The ISA doesn't say that M-mode means SBI. We try really hard to have SBI on all RISC-V, but I think KVM is taking it a bit too far. We can discuss how best to describe SBI, so userspace can choose to accelerate the M-mode in KVM, but I think that the ability to emulate M-mode in userspace should be provided.