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 xk+4OVNc 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 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 Fri, Feb 21, 2025 at 09:10:42AM -0800, Kalesh Singh wrote: > On Fri, Feb 21, 2025 at 4:05 AM Lorenzo Stoakes > wrote: > > > > Currently there is no means by which users can determine whether a given > > page in memory is in fact a guard region, that is having had the > > MADV_GUARD_INSTALL madvise() flag applied to it. > > > > This is intentional, as to provide this information in VMA metadata would > > contradict the intent of the feature (providing a means to change fault > > behaviour at a page table level rather than a VMA level), and would require > > VMA metadata operations to scan page tables, which is unacceptable. > > > > In many cases, users have no need to reflect and determine what regions > > have been designated guard regions, as it is the user who has established > > them in the first place. > > > > But in some instances, such as monitoring software, or software that relies > > upon being able to ascertain the nature of mappings within a remote process > > for instance, it becomes useful to be able to determine which pages have > > the guard region marker applied. > > > > This patch makes use of an unused pagemap bit (58) to provide this > > information. > > > > This patch updates the documentation at the same time as making the change > > such that the implementation of the feature and the documentation of it are > > tied together. > > > > Signed-off-by: Lorenzo Stoakes > > --- > > Documentation/admin-guide/mm/pagemap.rst | 3 ++- > > fs/proc/task_mmu.c | 6 +++++- > > 2 files changed, 7 insertions(+), 2 deletions(-) > > > > diff --git a/Documentation/admin-guide/mm/pagemap.rst b/Documentation/admin-guide/mm/pagemap.rst > > index caba0f52dd36..a297e824f990 100644 > > --- a/Documentation/admin-guide/mm/pagemap.rst > > +++ b/Documentation/admin-guide/mm/pagemap.rst > > @@ -21,7 +21,8 @@ There are four components to pagemap: > > * Bit 56 page exclusively mapped (since 4.2) > > * Bit 57 pte is uffd-wp write-protected (since 5.13) (see > > Documentation/admin-guide/mm/userfaultfd.rst) > > - * Bits 58-60 zero > > + * Bit 58 pte is a guard region (since 6.15) (see madvise (2) man page) > > Should this be 6.14 ? We're aiming for the 6.15 merge window so this is correct :>) I don't think this could be considered a hotfix haha! > > Other than that: Reviewed-by: Kalesh Singh Thanks! And thanks for review on the other patch also! Appreciated. > > Thanks, > Kalesh > > > + * Bits 59-60 zero > > * Bit 61 page is file-page or shared-anon (since 3.5) > > * Bit 62 page swapped > > * Bit 63 page present > > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c > > index f02cd362309a..c17615e21a5d 100644 > > --- a/fs/proc/task_mmu.c > > +++ b/fs/proc/task_mmu.c > > @@ -1632,6 +1632,7 @@ struct pagemapread { > > #define PM_SOFT_DIRTY BIT_ULL(55) > > #define PM_MMAP_EXCLUSIVE BIT_ULL(56) > > #define PM_UFFD_WP BIT_ULL(57) > > +#define PM_GUARD_REGION BIT_ULL(58) > > #define PM_FILE BIT_ULL(61) > > #define PM_SWAP BIT_ULL(62) > > #define PM_PRESENT BIT_ULL(63) > > @@ -1732,6 +1733,8 @@ static pagemap_entry_t pte_to_pagemap_entry(struct pagemapread *pm, > > page = pfn_swap_entry_to_page(entry); > > if (pte_marker_entry_uffd_wp(entry)) > > flags |= PM_UFFD_WP; > > + if (is_guard_swp_entry(entry)) > > + flags |= PM_GUARD_REGION; > > } > > > > if (page) { > > @@ -1931,7 +1934,8 @@ static const struct mm_walk_ops pagemap_ops = { > > * Bit 55 pte is soft-dirty (see Documentation/admin-guide/mm/soft-dirty.rst) > > * Bit 56 page exclusively mapped > > * Bit 57 pte is uffd-wp write-protected > > - * Bits 58-60 zero > > + * Bit 58 pte is a guard region > > + * Bits 59-60 zero > > * Bit 61 page is file-page or shared-anon > > * Bit 62 page swapped > > * Bit 63 page present > > -- > > 2.48.1 > >