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Tue, 17 Jun 2025 07:36:24 -0700 (PDT) Date: Tue, 17 Jun 2025 07:36:22 -0700 In-Reply-To: Mime-Version: 1.0 References: <50989f0a02790f9d7dc804c2ade6387c4e7fbdbc.1749634392.git.zhouquan@iscas.ac.cn> <20250611-352bef23df9a4ec55fe5cb68@orel> <20250612-70c2e573983d05c4fbc41102@orel> Message-ID: Subject: Re: [PATCH] RISC-V: KVM: Avoid re-acquiring memslot in kvm_riscv_gstage_map() From: Sean Christopherson To: Anup Patel Cc: Andrew Jones , zhouquan@iscas.ac.cn, anup@brainfault.org, atishp@atishpatra.org, paul.walmsley@sifive.com, palmer@dabbelt.com, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250617_073625_644637_4AEDCCF1 X-CRM114-Status: GOOD ( 13.80 ) 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-Type: text/plain; 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Tue, 17 Jun 2025 07:36:24 -0700 (PDT) Date: Tue, 17 Jun 2025 07:36:22 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <50989f0a02790f9d7dc804c2ade6387c4e7fbdbc.1749634392.git.zhouquan@iscas.ac.cn> <20250611-352bef23df9a4ec55fe5cb68@orel> <20250612-70c2e573983d05c4fbc41102@orel> Message-ID: Subject: Re: [PATCH] RISC-V: KVM: Avoid re-acquiring memslot in kvm_riscv_gstage_map() From: Sean Christopherson To: Anup Patel Cc: Andrew Jones , zhouquan@iscas.ac.cn, anup@brainfault.org, atishp@atishpatra.org, paul.walmsley@sifive.com, palmer@dabbelt.com, linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org, kvm@vger.kernel.org, kvm-riscv@lists.infradead.org Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Sun, Jun 15, 2025, Anup Patel wrote: > On Sat, Jun 14, 2025 at 3:59=E2=80=AFAM Sean Christopherson wrote: > > > > On Thu, Jun 12, 2025, Andrew Jones wrote: > > > On Wed, Jun 11, 2025 at 09:17:36AM -0700, Sean Christopherson wrote: > > > > Looks like y'all also have a bug where an -EEXIST will be returned = to userspace, > > > > and will generate what's probably a spurious kvm_err() message. > > > > > > On 32-bit riscv, due to losing the upper bits of the physical address= ? Or > > > is there yet another thing to fix? > > > > Another bug, I think. gstage_set_pte() returns -EEXIST if a PTE exists= , and I > > _assume_ that's supposed to be benign? But this code returns it blindl= y: >=20 > gstage_set_pte() returns -EEXIST only when it was expecting a non-leaf > PTE at a particular level but got a leaf PTE=20 Right, but isn't returning -EEXIST all the way to userspace undesirable beh= avior? E.g. in this sequence, KVM will return -EEXIST and incorrectly terminate th= e VM (assuming the VMM doesn't miraculously recover somehow): 1. Back the VM with HugeTLBFS 2. Fault-in memory, i.e. create hugepage mappings 3. Enable KVM_MEM_LOG_DIRTY_PAGES 4. Write-protection fault, kvm_riscv_gstage_map() tries to create a writab= le non-huge mapping. 5. gstage_set_pte() encounters the huge leaf PTE before reaching the targe= t level, and returns -EEXIST. AFAICT, gstage_wp_memory_region() doesn't split/shatter/demote hugepages, i= t simply clears _PAGE_WRITE. It's entirely possible I'm missing something that makes the above scenario impossible in practice, but at this point I'm genuinely curious :-) 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 1BF06C71136 for ; Tue, 17 Jun 2025 15:33:08 +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-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:Cc:To:From:Subject:Message-ID: References:Mime-Version:In-Reply-To:Date:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; 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