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[2003:d8:2f28:4900:2c24:4e20:1f21:9fbd]) by smtp.gmail.com with UTF8SMTPSA id 5b1f17b1804b1-4560c50b7b4sm100033485e9.25.2025.07.15.06.24.12 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Jul 2025 06:24:13 -0700 (PDT) From: David Hildenbrand To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, xen-devel@lists.xenproject.org, linux-fsdevel@vger.kernel.org, nvdimm@lists.linux.dev, David Hildenbrand , Andrew Morton , Juergen Gross , Stefano Stabellini , Oleksandr Tyshchenko , Dan Williams , Matthew Wilcox , Jan Kara , Alexander Viro , Christian Brauner , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Zi Yan , Baolin Wang , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Jann Horn , Pedro Falcato , Hugh Dickins , Oscar Salvador , Lance Yang , David Vrabel Subject: [PATCH v1 9/9] mm: rename vm_ops->find_special_page() to vm_ops->find_normal_page() Date: Tue, 15 Jul 2025 15:23:50 +0200 Message-ID: <20250715132350.2448901-10-david@redhat.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250715132350.2448901-1-david@redhat.com> References: <20250715132350.2448901-1-david@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: W6c3vOx4obTkLDBHgDDPju7QyowR5ZsenoyyUV_ro-I_1752585854 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true X-Stat-Signature: 5woz7ewpc7inwgdmhjf3qrq8rrec87g4 X-Rspamd-Queue-Id: E9CAAA000F X-Rspamd-Server: rspam10 X-Rspam-User: X-HE-Tag: 1752585857-927518 X-HE-Meta: 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 UhiIRylD ym/XhKgykwlZ37ck6+vfOZQ74zoqYOjl91QCh6KAz6bmv6CkPChnGDoA+7h2v4Jchj3mxezd3sTzIZCI54Irs0l/+/OzHVGasAvn9Mw8PhijtU3wF2oCDnbCWipu9JHKUWGk9E+y/Dk8bSNB61cHphuMZk+969e+S3rgZp0CsAlKISbJZx8sJIfV+nu7ByX3ZOxSKFaUdlchLz/tWCVA6mVXqxKWutZwATd2rqDVirQjx/xFi2PrM4XSzVtoyybm1VxlrNojcQKSjR6tdrGhLAntefUn9eF2LTGMf5wE02apV75Y3gT0M3BvnyWCxSyAL8Oo5WUy+Ra61rPvMe+8zlIdO5uFWoiCevmCHFU3gmwIX7hp7bCbBZD9YO6+hd1Vr+6pBSEU+YhRPSbLAkczUjv0qsW2Fbx8pffMo4okCfPBrX3qsdr14xYFHJUFaH/5nz96q2CqFRqyh0b/XKUpDbKm6oA1FoWqmFmxmhu2rkDERjdJtwwdjh5N+4hQ4OZFd19Fl3UmLlTWstuXeWgKvZG0q8YuwdwVnaJzRxrrv/qpmYoE7pKg1KM9mrOV6myY/a8gkiZyAnEgTEGrY4S5dnR9bVnyNeF4nR44yOfGcK90tvE8tc7m8RLfR3g== 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: ... and hide it behind a kconfig option. There is really no need for any !xen code to perform this check. The naming is a bit off: we want to find the "normal" page when a PTE was marked "special". So it's really not "finding a special" page. Improve the documentation, and add a comment in the code where XEN ends up performing the pte_mkspecial() through a hypercall. More details can be found in commit 923b2919e2c3 ("xen/gntdev: mark userspace PTEs as special on x86 PV guests"). Cc: David Vrabel Signed-off-by: David Hildenbrand --- drivers/xen/Kconfig | 1 + drivers/xen/gntdev.c | 5 +++-- include/linux/mm.h | 18 +++++++++++++----- mm/Kconfig | 2 ++ mm/memory.c | 12 ++++++++++-- tools/testing/vma/vma_internal.h | 18 +++++++++++++----- 6 files changed, 42 insertions(+), 14 deletions(-) diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig index 24f485827e039..f9a35ed266ecf 100644 --- a/drivers/xen/Kconfig +++ b/drivers/xen/Kconfig @@ -138,6 +138,7 @@ config XEN_GNTDEV depends on XEN default m select MMU_NOTIFIER + select FIND_NORMAL_PAGE help Allows userspace processes to use grants. diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c index 61faea1f06630..d1bc0dae2cdf9 100644 --- a/drivers/xen/gntdev.c +++ b/drivers/xen/gntdev.c @@ -309,6 +309,7 @@ static int find_grant_ptes(pte_t *pte, unsigned long addr, void *data) BUG_ON(pgnr >= map->count); pte_maddr = arbitrary_virt_to_machine(pte).maddr; + /* Note: this will perform a pte_mkspecial() through the hypercall. */ gnttab_set_map_op(&map->map_ops[pgnr], pte_maddr, flags, map->grants[pgnr].ref, map->grants[pgnr].domid); @@ -516,7 +517,7 @@ static void gntdev_vma_close(struct vm_area_struct *vma) gntdev_put_map(priv, map); } -static struct page *gntdev_vma_find_special_page(struct vm_area_struct *vma, +static struct page *gntdev_vma_find_normal_page(struct vm_area_struct *vma, unsigned long addr) { struct gntdev_grant_map *map = vma->vm_private_data; @@ -527,7 +528,7 @@ static struct page *gntdev_vma_find_special_page(struct vm_area_struct *vma, static const struct vm_operations_struct gntdev_vmops = { .open = gntdev_vma_open, .close = gntdev_vma_close, - .find_special_page = gntdev_vma_find_special_page, + .find_normal_page = gntdev_vma_find_normal_page, }; /* ------------------------------------------------------------------ */ diff --git a/include/linux/mm.h b/include/linux/mm.h index 6877c894fe526..cc3322fce62f4 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -646,13 +646,21 @@ struct vm_operations_struct { struct mempolicy *(*get_policy)(struct vm_area_struct *vma, unsigned long addr, pgoff_t *ilx); #endif +#ifdef CONFIG_FIND_NORMAL_PAGE /* - * Called by vm_normal_page() for special PTEs to find the - * page for @addr. This is useful if the default behavior - * (using pte_page()) would not find the correct page. + * Called by vm_normal_page() for special PTEs in @vma at @addr. This + * allows for returning a "normal" page from vm_normal_page() even + * though the PTE indicates that the "struct page" either does not exist + * or should not be touched: "special". + * + * Do not add new users: this really only works when a "normal" page + * was mapped, but then the PTE got changed to something weird (+ + * marked special) that would not make pte_pfn() identify the originally + * inserted page. */ - struct page *(*find_special_page)(struct vm_area_struct *vma, - unsigned long addr); + struct page *(*find_normal_page)(struct vm_area_struct *vma, + unsigned long addr); +#endif /* CONFIG_FIND_NORMAL_PAGE */ }; #ifdef CONFIG_NUMA_BALANCING diff --git a/mm/Kconfig b/mm/Kconfig index 0287e8d94aea7..82c281b4f6937 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -1397,6 +1397,8 @@ config PT_RECLAIM Note: now only empty user PTE page table pages will be reclaimed. +config FIND_NORMAL_PAGE + def_bool n source "mm/damon/Kconfig" diff --git a/mm/memory.c b/mm/memory.c index f1834a19a2f1e..d09f2ff4a866e 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -619,6 +619,12 @@ static void print_bad_page_map(struct vm_area_struct *vma, * trivial. Secondly, an architecture may not have a spare page table * entry bit, which requires a more complicated scheme, described below. * + * With CONFIG_FIND_NORMAL_PAGE, we might have the "special" bit set on + * page table entries that actually map "normal" pages: however, that page + * cannot be looked up through the PFN stored in the page table entry, but + * instead will be looked up through vm_ops->find_normal_page(). So far, this + * only applies to PTEs. + * * A raw VM_PFNMAP mapping (ie. one that is not COWed) is always considered a * special mapping (even if there are underlying and valid "struct pages"). * COWed pages of a VM_PFNMAP are always normal. @@ -716,8 +722,10 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, unsigned long pfn = pte_pfn(pte); if (unlikely(pte_special(pte))) { - if (vma->vm_ops && vma->vm_ops->find_special_page) - return vma->vm_ops->find_special_page(vma, addr); +#ifdef CONFIG_FIND_NORMAL_PAGE + if (vma->vm_ops && vma->vm_ops->find_normal_page) + return vma->vm_ops->find_normal_page(vma, addr); +#endif /* CONFIG_FIND_NORMAL_PAGE */ if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)) return NULL; if (is_zero_pfn(pfn)) diff --git a/tools/testing/vma/vma_internal.h b/tools/testing/vma/vma_internal.h index 991022e9e0d3b..9eecfb1dcc13f 100644 --- a/tools/testing/vma/vma_internal.h +++ b/tools/testing/vma/vma_internal.h @@ -465,13 +465,21 @@ struct vm_operations_struct { struct mempolicy *(*get_policy)(struct vm_area_struct *vma, unsigned long addr, pgoff_t *ilx); #endif +#ifdef CONFIG_FIND_NORMAL_PAGE /* - * Called by vm_normal_page() for special PTEs to find the - * page for @addr. This is useful if the default behavior - * (using pte_page()) would not find the correct page. + * Called by vm_normal_page() for special PTEs in @vma at @addr. This + * allows for returning a "normal" page from vm_normal_page() even + * though the PTE indicates that the "struct page" either does not exist + * or should not be touched: "special". + * + * Do not add new users: this really only works when a "normal" page + * was mapped, but then the PTE got changed to something weird (+ + * marked special) that would not make pte_pfn() identify the originally + * inserted page. */ - struct page *(*find_special_page)(struct vm_area_struct *vma, - unsigned long addr); + struct page *(*find_normal_page)(struct vm_area_struct *vma, + unsigned long addr); +#endif /* CONFIG_FIND_NORMAL_PAGE */ }; struct vm_unmapped_area_info { -- 2.50.1