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charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 From: Nikita Kalyazin =0A= =0A= Let's provide folio_{zap,restore}_direct_map helpers as preparation for=0A= supporting removal of the direct map for guest_memfd folios.=0A= In folio_zap_direct_map(), flush TLB to make sure the data is not=0A= accessible.=0A= =0A= The new helpers need to be accessible to KVM on architectures that=0A= support guest_memfd (x86 and arm64).=0A= =0A= Direct map removal gives guest_memfd the same protection that=0A= memfd_secret does, such as hardening against Spectre-like attacks=0A= through in-kernel gadgets.=0A= =0A= Signed-off-by: Nikita Kalyazin =0A= ---=0A= include/linux/set_memory.h | 13 ++++++++++++=0A= mm/memory.c | 42 ++++++++++++++++++++++++++++++++++++++=0A= 2 files changed, 55 insertions(+)=0A= =0A= diff --git a/include/linux/set_memory.h b/include/linux/set_memory.h=0A= index 1a2563f525fc..24caea2931f9 100644=0A= --- a/include/linux/set_memory.h=0A= +++ b/include/linux/set_memory.h=0A= @@ -41,6 +41,15 @@ static inline int set_direct_map_valid_noflush(const voi= d *addr,=0A= return 0;=0A= }=0A= =0A= +static inline int folio_zap_direct_map(struct folio *folio)=0A= +{=0A= + return 0;=0A= +}=0A= +=0A= +static inline void folio_restore_direct_map(struct folio *folio)=0A= +{=0A= +}=0A= +=0A= static inline bool kernel_page_present(struct page *page)=0A= {=0A= return true;=0A= @@ -57,6 +66,10 @@ static inline bool can_set_direct_map(void)=0A= }=0A= #define can_set_direct_map can_set_direct_map=0A= #endif=0A= +=0A= +int folio_zap_direct_map(struct folio *folio);=0A= +void folio_restore_direct_map(struct folio *folio);=0A= +=0A= #endif /* CONFIG_ARCH_HAS_SET_DIRECT_MAP */=0A= =0A= #ifdef CONFIG_X86_64=0A= diff --git a/mm/memory.c b/mm/memory.c=0A= index 07778814b4a8..cab6bb237fc0 100644=0A= --- a/mm/memory.c=0A= +++ b/mm/memory.c=0A= @@ -78,6 +78,7 @@=0A= #include =0A= #include =0A= #include =0A= +#include =0A= =0A= #include =0A= =0A= @@ -7478,3 +7479,44 @@ void vma_pgtable_walk_end(struct vm_area_struct *vma= )=0A= if (is_vm_hugetlb_page(vma))=0A= hugetlb_vma_unlock_read(vma);=0A= }=0A= +=0A= +#ifdef CONFIG_ARCH_HAS_SET_DIRECT_MAP=0A= +/**=0A= + * folio_zap_direct_map - remove a folio from the kernel direct map=0A= + * @folio: folio to remove from the direct map=0A= + *=0A= + * Removes the folio from the kernel direct map and flushes the TLB. This= may=0A= + * require splitting huge pages in the direct map, which can fail due to m= emory=0A= + * allocation.=0A= + *=0A= + * Return: 0 on success, or a negative error code on failure.=0A= + */=0A= +int folio_zap_direct_map(struct folio *folio)=0A= +{=0A= + const void *addr =3D folio_address(folio);=0A= + int ret;=0A= +=0A= + ret =3D set_direct_map_valid_noflush(addr, folio_nr_pages(folio), false);= =0A= + flush_tlb_kernel_range((unsigned long)addr,=0A= + (unsigned long)addr + folio_size(folio));=0A= +=0A= + return ret;=0A= +}=0A= +EXPORT_SYMBOL_FOR_MODULES(folio_zap_direct_map, "kvm");=0A= +=0A= +/**=0A= + * folio_restore_direct_map - restore the kernel direct map entry for a fo= lio=0A= + * @folio: folio whose direct map entry is to be restored=0A= + *=0A= + * This may only be called after a prior successful folio_zap_direct_map()= on=0A= + * the same folio. Because the zap will have already split any huge pages= in=0A= + * the direct map, restoration here only updates protection bits and canno= t=0A= + * fail.=0A= + */=0A= +void folio_restore_direct_map(struct folio *folio)=0A= +{=0A= + WARN_ON_ONCE(set_direct_map_valid_noflush(folio_address(folio),=0A= + folio_nr_pages(folio), true));=0A= +}=0A= +EXPORT_SYMBOL_FOR_MODULES(folio_restore_direct_map, "kvm");=0A= +#endif /* CONFIG_ARCH_HAS_SET_DIRECT_MAP */=0A= -- =0A= 2.50.1=0A= =0A=