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[99.254.144.39]) by smtp.gmail.com with ESMTPSA id ew5-20020a05622a514500b00400a760cbfdsm12611511qtb.17.2023.07.05.09.38.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 Jul 2023 09:38:26 -0700 (PDT) Date: Wed, 5 Jul 2023 12:38:24 -0400 From: Peter Xu To: James Houghton Cc: Axel Rasmussen , Alexander Viro , Andrew Morton , Christian Brauner , David Hildenbrand , Huang Ying , Hugh Dickins , Jiaqi Yan , Jonathan Corbet , "Liam R. Howlett" , Miaohe Lin , Mike Kravetz , "Mike Rapoport (IBM)" , Muchun Song , Nadav Amit , Naoya Horiguchi , Shuah Khan , ZhangPeng , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v2 1/6] mm: userfaultfd: add new UFFDIO_POISON ioctl Message-ID: References: <20230629205040.665834-1-axelrasmussen@google.com> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: dearnon34o16o588kr6tx17yisbmbcoh X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: BC3D24000E X-HE-Tag: 1688575109-283742 X-HE-Meta: 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 zQ2Qhv2V VDRiCfYmDz6yL4cNWE193QPCvE7xIZ2WUd+nD6JbtWH97t9y+d6YAOJKjW+bjuf31oqSvDSn+KFRZsnp0BJrWUm+jwvR/NVxqCWwAYds8zvoIC7XNCBMvasXkFvr5NOD0ILsrXVzdjas1PJvVde+0E7i1MLfaG5I8OspFDjR9D1z80SWAcSF7L0h/LUlVj2GPF0zssztQPQ0Q1H0YtAtu997YqQ2pZ5eI+YfngNJJv997rRwlcRYd/IAtWA2RSNPnvo9T9+gXQrnK4d4WWMqefYVV2XAF4JJ2w5EpGzgbc1xk3LqH48rU9YR/9vzZv2VTKznRd+WDc7Xxv97CEfQHbgAYmENAf9waU4Ptg/4jYs8APLxlHUPEtM4T63OfxRHy4zN66fIFomsR6HqbqyvfLwVe3bqr5E6+sT7V5es+nMf4z2RNs1AIWdz7aw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jul 05, 2023 at 09:27:15AM -0700, James Houghton wrote: > On Wed, Jul 5, 2023 at 9:15 AM Peter Xu wrote: > > > > On Wed, Jul 05, 2023 at 09:09:19AM -0700, James Houghton wrote: > > > > > diff --git a/include/linux/swapops.h b/include/linux/swapops.h > > > > > index 4c932cb45e0b..8259fee32421 100644 > > > > > --- a/include/linux/swapops.h > > > > > +++ b/include/linux/swapops.h > > > > > @@ -394,7 +394,8 @@ typedef unsigned long pte_marker; > > > > > > > > > > #define PTE_MARKER_UFFD_WP BIT(0) > > > > > #define PTE_MARKER_SWAPIN_ERROR BIT(1) > > > > > -#define PTE_MARKER_MASK (BIT(2) - 1) > > > > > +#define PTE_MARKER_UFFD_POISON BIT(2) > > > > > > > > One more tab. > > > > > > > > Though I remembered the last time we discussed IIRC we plan to rename > > > > SWAPIN_ERROR and reuse it, could you explain why a new bit is still needed? > > > > > > > > I think I commented this but I'll do it again: IIUC any existing host > > > > swapin errors for guest pages should be reported as MCE too, afaict, > > > > happened in kvm context. > > > > > > I think swapin errors are treated differently than poison. Swapin > > > errors get VM_FAULT_SIGBUS, and poison gets VM_FAULT_HWPOISON, so > > > UFFDIO_POISON should also get VM_FAULT_HWPOISON (so that's what Axel > > > has implemented). And I think that needs a separate PTE marker. > > > > My question was, should we also make SWAPIN_ERROR return VM_FAULT_HWPOISON > > always? > > > > Just to recap from what I already commented above - if a guest page got > > error in swapin due to block sector failures, it should be treated as > > VM_FAULT_HWPOISON too, IMHO. IOW, I think current SWAPIN_ERROR is wrong > > when in kvm context and we should fix it first. > > Oh! Yes, I agree, though I'm not familiar enough with the users of > SWAPIN_ERROR to know if we can actually make this change. Miaohe initially proposed this swapin error facility, let's see whether he can comment; he's already in the cc list. AFAICT that's the right thing to do, and it shouldn't affect any existing user of swapin error if there is. Or say, VM_FAULT_HWPOISON should be the same as VM_FAULT_SIGBUS when not in kvm context, so shouldn't change a thing in !kvm, while changing that should fix kvm from crashing a guest where we shouldn't need to. -- Peter Xu