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[2003:cb:c706:1700:6b81:27cb:c9e2:a09a]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3730814602asm14910248f8f.44.2024.08.28.00.44.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 28 Aug 2024 00:44:05 -0700 (PDT) Message-ID: <9f9d7e96-b135-4830-b528-37418ae7bbfd@redhat.com> Date: Wed, 28 Aug 2024 09:44:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 06/19] mm/pagewalk: Check pfnmap for folio_walk_start() To: Peter Xu , linux-kernel@vger.kernel.org, linux-mm@kvack.org Cc: Gavin Shan , Catalin Marinas , x86@kernel.org, Ingo Molnar , Andrew Morton , Paolo Bonzini , Dave Hansen , Thomas Gleixner , Alistair Popple , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Sean Christopherson , Oscar Salvador , Jason Gunthorpe , Borislav Petkov , Zi Yan , Axel Rasmussen , Yan Zhao , Will Deacon , Kefeng Wang , Alex Williamson References: <20240826204353.2228736-1-peterx@redhat.com> <20240826204353.2228736-7-peterx@redhat.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: CA70980005 X-Stat-Signature: wmuahqxbsjndotceppfeihfcwoij3gzc X-Rspam-User: X-HE-Tag: 1724831051-118078 X-HE-Meta: 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 wLk6Ym1h KZ68yx4U7ofn8ozysTI87QIs27iTgbzMLXCatt1iAocJPhPEVmpFbb3rEhL7m/UKFxXCIsCBHD6VxVLhqwW1FZdFZuWeRg99530k/5TEnzQ5SfO3CvDEbW+rvd+ECiUM7gAfCCV3OxZNmXyE1mippjI+lQ5cU1OQIx0aECg3ZeUfDQ6kmZo9AGFcGjtFnKY87aY0E/RL5NzMTxY/mw8nmwuDD8QiDFtLdchyf/8x5SjcTHlJ2fpQKcuwinnYQl2r4Qj469xR/edo5wVs1CMaOLco0Yrei434JJvMixK4eemK5Bd3PSU/LuQSHUmd0TPoc3dcBi8YsrSPbFm7RwUACp/pPJSezFpyymrD3VPp/LAQr1qI6pzvYLyTnqNj8nsd0i3uTB+L4IiIzGuDloPR6zqxgNuSIEpY+qpvwSi0X4xFjho0WxECEOihvrTmKDLnM4Cq2GwTwMPMIIDqVJ9wioEX8cg== 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: List-Subscribe: List-Unsubscribe: On 26.08.24 22:43, Peter Xu wrote: > Teach folio_walk_start() to recognize special pmd/pud mappings, and fail > them properly as it means there's no folio backing them. > > Cc: David Hildenbrand > Signed-off-by: Peter Xu > --- > mm/pagewalk.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/pagewalk.c b/mm/pagewalk.c > index cd79fb3b89e5..12be5222d70e 100644 > --- a/mm/pagewalk.c > +++ b/mm/pagewalk.c > @@ -753,7 +753,7 @@ struct folio *folio_walk_start(struct folio_walk *fw, > fw->pudp = pudp; > fw->pud = pud; > > - if (!pud_present(pud) || pud_devmap(pud)) { > + if (!pud_present(pud) || pud_devmap(pud) || pud_special(pud)) { > spin_unlock(ptl); > goto not_found; > } else if (!pud_leaf(pud)) { > @@ -783,7 +783,7 @@ struct folio *folio_walk_start(struct folio_walk *fw, > fw->pmdp = pmdp; > fw->pmd = pmd; > > - if (pmd_none(pmd)) { > + if (pmd_none(pmd) || pmd_special(pmd)) { > spin_unlock(ptl); > goto not_found; > } else if (!pmd_leaf(pmd)) { As raised, this is not the right way to to it. You should follow what CONFIG_ARCH_HAS_PTE_SPECIAL and vm_normal_page() does. It's even spelled out in vm_normal_page_pmd() that at the time it was introduced there was no pmd_special(), so there was no way to handle that. diff --git a/mm/memory.c b/mm/memory.c index f0cf5d02b4740..272445e9db147 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -672,15 +672,29 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr, { unsigned long pfn = pmd_pfn(pmd); - /* - * There is no pmd_special() but there may be special pmds, e.g. - * in a direct-access (dax) mapping, so let's just replicate the - * !CONFIG_ARCH_HAS_PTE_SPECIAL case from vm_normal_page() here. - */ + if (IS_ENABLED(CONFIG_ARCH_HAS_PMD_SPECIAL)) { + if (likely(!pmd_special(pmd))) + goto check_pfn; + if (vma->vm_ops && vma->vm_ops->find_special_page) + return vma->vm_ops->find_special_page(vma, addr); + if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)) + return NULL; + if (is_huge_zero_pmd(pmd)) + return NULL; + if (pmd_devmap(pmd)) + /* See vm_normal_page() */ + return NULL; + return NULL; + } + + /* !CONFIG_ARCH_HAS_PMD_SPECIAL case follows: */ + if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) { if (vma->vm_flags & VM_MIXEDMAP) { if (!pfn_valid(pfn)) return NULL; + if (is_huge_zero_pmd(pmd)) + return NULL; goto out; } else { unsigned long off; @@ -692,6 +706,11 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr, } } + /* + * For historical reasons, these might not have pmd_special() set, + * so we'll check them manually, in contrast to vm_normal_page(). + */ +check_pfn: if (pmd_devmap(pmd)) return NULL; if (is_huge_zero_pmd(pmd)) We should then look into mapping huge zeropages also with pmd_special. pmd_devmap we'll leave alone until removed. But that's indeoendent of your series. I wonder if CONFIG_ARCH_HAS_PTE_SPECIAL is sufficient and we don't need additional CONFIG_ARCH_HAS_PMD_SPECIAL. As I said, if you need someone to add vm_normal_page_pud(), I can handle that. -- Cheers, David / dhildenb