From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id ECF96C54ED1 for ; Fri, 23 May 2025 17:46:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Content-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To:Subject: MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=UiGa7go98pfD5Rgj8UAHYhIXW8aJ999PuOPy7csigQU=; b=heti1Jq4Akai1n vr7P5P0zIk7F71ADVtFZlioEbjsOezgdHker8CwgAsIFQKtF64ftC+poCjN7QRR7LVOcCMN8rhwJc gXkfJ7tofivJA4htmUzskQIT4zat2Q8HiKVoZ1YaE/w/wsRMxMRJBna8Rd7GlVAUI0QeLyxJyzPhG P6sQc4GgYdH8EZzyObFuoMd03iq4YgahRWpgo075bkx7/p7dL0JXKJvU2HRRN8eHv914CO6iP9oY3 0yg7SbfYi7wCyr8t/Hc/3oklRA//Ax0/Uv1LKVLxugfLOYjbXjSxMdm3FF9PUFAoenfL+eDvnYLSc N7tRZq+xu9wRP2iPx/LA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uIWTJ-00000004as3-2qME; Fri, 23 May 2025 17:46:17 +0000 Received: from out-172.mta1.migadu.com ([95.215.58.172]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1uIWRz-00000004aYt-1l5A for kvm-riscv@lists.infradead.org; Fri, 23 May 2025 17:44:56 +0000 Message-ID: <7ad8cfad-745f-4626-a2ce-eab33998a711@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1748022283; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=rQan1lP1SvjQ3YoRxtVwG6BShbKuywXf8Ct5XNCQIOg=; b=NAYkbMnBv2evElrcBOFds8eWgU1fYgMA3/0NEOiNFfz9SqkvlWQGDOpCmog0ZWqn9eNse8 fgii+JDcSH7sb67ucwZRsWTjlg7ojV58E/jfFNqNTcCx/JnTYuL4z8vytXAqUB3iq1OggA 4d+3iHUV/8HVnz+o13xmZw9cjoW8J+s= Date: Fri, 23 May 2025 10:44:37 -0700 MIME-Version: 1.0 Subject: Re: [PATCH v3 0/2] RISC-V: KVM: VCPU reset fixes To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Anup Patel Cc: kvm-riscv@lists.infradead.org, kvm@vger.kernel.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Anup Patel , Atish Patra , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Andrew Jones References: <20250515143723.2450630-4-rkrcmar@ventanamicro.com> <1a7a81fd-cf15-4b54-a805-32d66ced4517@linux.dev> Content-Language: en-US X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Atish Patra In-Reply-To: X-Migadu-Flow: FLOW_OUT X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250523_104455_602398_86A4D3C1 X-CRM114-Status: GOOD ( 24.11 ) X-BeenThere: kvm-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: base64 Content-Type: text/plain; charset="utf-8"; Format="flowed" Sender: "kvm-riscv" Errors-To: kvm-riscv-bounces+kvm-riscv=archiver.kernel.org@lists.infradead.org Ck9uIDUvMjMvMjUgMjoyMCBBTSwgUmFkaW0gS3LEjW3DocWZIHdyb3RlOgo+IDIwMjUtMDUtMjNU MTM6Mzg6MjYrMDU6MzAsIEFudXAgUGF0ZWwgPGFwYXRlbEB2ZW50YW5hbWljcm8uY29tPjoKPj4g T24gRnJpLCBNYXkgMjMsIDIwMjUgYXQgMTI6NDfigK9QTSBSYWRpbSBLcsSNbcOhxZkgPHJrcmNt YXJAdmVudGFuYW1pY3JvLmNvbT4gd3JvdGU6Cj4+PiAyMDI1LTA1LTIyVDE0OjQzOjQwLTA3OjAw LCBBdGlzaCBQYXRyYSA8YXRpc2gucGF0cmFAbGludXguZGV2PjoKPj4+PiBPbiA1LzE1LzI1IDc6 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to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=rQan1lP1SvjQ3YoRxtVwG6BShbKuywXf8Ct5XNCQIOg=; b=NAYkbMnBv2evElrcBOFds8eWgU1fYgMA3/0NEOiNFfz9SqkvlWQGDOpCmog0ZWqn9eNse8 fgii+JDcSH7sb67ucwZRsWTjlg7ojV58E/jfFNqNTcCx/JnTYuL4z8vytXAqUB3iq1OggA 4d+3iHUV/8HVnz+o13xmZw9cjoW8J+s= Date: Fri, 23 May 2025 10:44:37 -0700 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH v3 0/2] RISC-V: KVM: VCPU reset fixes To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Anup Patel Cc: kvm-riscv@lists.infradead.org, kvm@vger.kernel.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Anup Patel , Atish Patra , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Andrew Jones References: <20250515143723.2450630-4-rkrcmar@ventanamicro.com> <1a7a81fd-cf15-4b54-a805-32d66ced4517@linux.dev> 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From: Atish Patra In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 5/23/25 2:20 AM, Radim Krčmář wrote: > 2025-05-23T13:38:26+05:30, Anup Patel : >> On Fri, May 23, 2025 at 12:47 PM Radim Krčmář wrote: >>> 2025-05-22T14:43:40-07:00, Atish Patra : >>>> On 5/15/25 7:37 AM, Radim KrÄmáŠwrote: >>>>> Hello, >>>>> >>>>> the design still requires a discussion. >>>>> >>>>> [v3 1/2] removes most of the additional changes that the KVM capability >>>>> was doing in v2. [v3 2/2] is new and previews a general solution to the >>>>> lack of userspace control over KVM SBI. >>>>> >>>> I am still missing the motivation behind it. If the motivation is SBI >>>> HSM suspend, the PATCH2 doesn't achieve that as it forwards every call >>>> to the user space. Why do you want to control hsm start/stop from the >>>> user space ? >>> HSM needs fixing, because KVM doesn't know what the state after >>> sbi_hart_start should be. >>> For example, we had a discussion about scounteren and regardless of what >>> default we choose in KVM, the userspace might want a different value. >>> I don't think that HSM start/stop is a hot path, so trapping to >>> userspace seems better than adding more kernel code. >> There are no implementation specific S-mode CSR reset values >> required at the moment. > Jessica mentioned that BSD requires scounteren to be non-zero, so > userspace should be able to provide that value. Jessica admitted that it was a bug which should be fixed. > I would prefer if KVM could avoid getting into those discussions. > We can just just let userspace be as crazy as it wants. The scounteren state you mentioned is already fixed now. I would prefer to do this if there are more of these issues. Otherwise, we may gain little by just delegating more work to the userspace for no reason. >> Whenever the need arises, we will extend >> the ONE_REG interface so that user space can specify custom >> CSR reset values at Guest/VM creation time. We don't need to >> forward SBI HSM calls to user space for custom S-mode CSR >> reset values. > The benefits of adding a new ONE_REG interface seem very small compared > to the drawbacks of having extra kernel code. How ? The extra kernel code is just few lines where it just registers a SBI extension and forwards it to the userspace. That's for the entire extension. For extensions like HSM, only selective functions that should be forwarded to the userspace which defeats the purpose. Let's not try to fix something that is not broken yet. > If userspace would want to reset or setup new multi-VCPUs VMs often, we > could add an interface that loads the whole register state from > userspace in a single IOCTL, because ONE_REG is not the best interface > for bulk data transfer either. > >>> Forwarding all the unimplemented SBI ecalls shouldn't be a performance >>> issue, because S-mode software would hopefully learn after the first >>> error and stop trying again. >>> >>> Allowing userspace to fully implement the ecall instruction one of the >>> motivations as well -- SBI is not a part of RISC-V ISA, so someone might >>> be interested in accelerating a different M-mode software with KVM. >>> >>> I'll send v4 later today -- there is a missing part in [2/2], because >>> userspace also needs to be able to emulate the base SBI extension. >>> >> [...] The best approach is to selectively forward SBI >> calls to user space where needed (e.g. SBI system reset, >> SBI system suspend, SBI debug console, etc.). > That is exactly what my proposal does, it's just that the userspace says > what is "needed". > > If we started with this mechanism, KVM would not have needed to add > SRST/SUSP/DBCN SBI emulation at all -- they would be forwarded as any > other unhandled ecall. 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