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([2a01:e0a:e17:9700:16d2:7456:6634:9626]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-231d4af1b75sm127752175ad.85.2025.05.23.12.23.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 23 May 2025 12:23:53 -0700 (PDT) Message-ID: <01696003-e2b4-4450-85cf-715e31b136d5@rivosinc.com> Date: Fri, 23 May 2025 21:23:41 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 13/14] RISC-V: KVM: add support for FWFT SBI extension To: Atish Patra , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Paul Walmsley , Palmer Dabbelt , Anup Patel , Atish Patra , Shuah Khan , Jonathan Corbet , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-kselftest@vger.kernel.org Cc: Samuel Holland , Andrew Jones , Deepak Gupta , Charlie Jenkins , linux-riscv References: <20250523101932.1594077-1-cleger@rivosinc.com> <20250523101932.1594077-14-cleger@rivosinc.com> <9f9e2869-725d-4590-887a-9b0ef091472e@rivosinc.com> <5dd587b3-8c04-41d1-b677-5b07266cfec5@linux.dev> Content-Language: en-US From: =?UTF-8?B?Q2zDqW1lbnQgTMOpZ2Vy?= In-Reply-To: <5dd587b3-8c04-41d1-b677-5b07266cfec5@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 23/05/2025 20:02, Atish Patra wrote: > On 5/23/25 9:27 AM, Radim KrÄmáŠwrote: >> 2025-05-23T17:29:49+02:00, Clément Léger : >>> On 23/05/2025 15:05, Radim Krčmář wrote: >>>> 2025-05-23T12:19:30+02:00, Clément Léger : >>>>> +++ 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. >> >> Sounds fine. >> > > Yeah. We can have a follow up series for SBI FWFT state that allows user > space to toggle each state individually. > >>> 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. >> >> Not blocking, but I would at least default FWFT to disabled, because >> current userspace cannot handle [14/14].  (Well... save/restore was >> probably broken even before, but let's try to not make it worse. :]) >> > > User space can not enable or disable misaligned access delegation as > there is no interface for now rightly pointed by you. I guess supporting > that would be quicker than fixing the broader guest save/restore > anyways. Isn't it ? > > We can have the patches ready for the next MW for FWFT one reg interface. Yeah sure I'll work on that in the meantime. > >> Thanks. >> >> _______________________________________________ >> linux-riscv mailing list >> linux-riscv@lists.infradead.org >> http://lists.infradead.org/mailman/listinfo/linux-riscv >