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Mon, 26 May 2025 01:58:47 -0700 (PDT) Precedence: bulk X-Mailing-List: kvm@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: Mon, 26 May 2025 10:58:46 +0200 Message-Id: Subject: Re: [PATCH v8 13/14] RISC-V: KVM: add support for FWFT SBI extension Cc: "Samuel Holland" , "Andrew Jones" , "Deepak Gupta" , "Charlie Jenkins" , "linux-riscv" To: "Atish Patra" , =?utf-8?q?Cl=C3=A9ment_L=C3=A9ger?= , "Paul Walmsley" , "Palmer Dabbelt" , "Anup Patel" , "Atish Patra" , "Shuah Khan" , "Jonathan Corbet" , , , , , , From: =?utf-8?q?Radim_Kr=C4=8Dm=C3=A1=C5=99?= 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> In-Reply-To: <5dd587b3-8c04-41d1-b677-5b07266cfec5@linux.dev> 2025-05-23T11:02:11-07:00, Atish Patra : > On 5/23/25 9:27 AM, Radim Kr=C3=84m=C3=83=C2=A1=C3=85 wrote: >> 2025-05-23T17:29:49+02:00, Cl=C3=A9ment L=C3=A9ger = : >>> 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. >>=20 >> 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. :]) >>=20 > > User space can not enable or disable misaligned access delegation as=20 > there is no interface for now rightly pointed by you. I mean setting default_disabled=3Dtrue and just disabling FWFT for the guest unless userspace explicitly enables the incomplete extension. We would blame the user for wanting mutually exclusive features. > I guess supporting= =20 > that would be quicker than fixing the broader guest save/restore=20 > anyways. Isn't it ? Yes. The save/restore for FWFT is simple (if we disregard the discussions), but definitely more than a single line.