[PATCH v9 01/13] set_memory: add folio_{zap, restore}_direct_map helpers
Nikita Kalyazin
kalyazin at amazon.com
Thu Jan 15 03:03:56 PST 2026
On 15/01/2026 10:54, Huacai Chen wrote:
> Hi, Nikita,
Hi Huacai,
>
> On Wed, Jan 14, 2026 at 9:45 PM Kalyazin, Nikita <kalyazin at amazon.co.uk> wrote:
>>
>> From: Nikita Kalyazin <kalyazin at amazon.com>
>>
>> These allow guest_memfd to remove its memory from the direct map.
>> Only implement them for architectures that have direct map.
>> In folio_zap_direct_map(), flush TLB on architectures where
>> set_direct_map_valid_noflush() does not flush it internally.
>>
>> The new helpers need to be accessible to KVM on architectures that
>> support guest_memfd (x86 and arm64). Since arm64 does not support
>> building KVM as a module, only export them on x86.
>>
>> Direct map removal gives guest_memfd the same protection that
>> memfd_secret does, such as hardening against Spectre-like attacks
>> through in-kernel gadgets.
>>
>> Signed-off-by: Nikita Kalyazin <kalyazin at amazon.com>
>> ---
>> arch/arm64/include/asm/set_memory.h | 2 ++
>> arch/arm64/mm/pageattr.c | 12 ++++++++++++
>> arch/loongarch/include/asm/set_memory.h | 2 ++
>> arch/loongarch/mm/pageattr.c | 16 ++++++++++++++++
>> arch/riscv/include/asm/set_memory.h | 2 ++
>> arch/riscv/mm/pageattr.c | 16 ++++++++++++++++
>> arch/s390/include/asm/set_memory.h | 2 ++
>> arch/s390/mm/pageattr.c | 18 ++++++++++++++++++
>> arch/x86/include/asm/set_memory.h | 2 ++
>> arch/x86/mm/pat/set_memory.c | 20 ++++++++++++++++++++
>> include/linux/set_memory.h | 10 ++++++++++
>> 11 files changed, 102 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/set_memory.h b/arch/arm64/include/asm/set_memory.h
>> index 90f61b17275e..d949f1deb701 100644
>> --- a/arch/arm64/include/asm/set_memory.h
>> +++ b/arch/arm64/include/asm/set_memory.h
>> @@ -14,6 +14,8 @@ int set_memory_valid(unsigned long addr, int numpages, int enable);
>> int set_direct_map_invalid_noflush(struct page *page);
>> int set_direct_map_default_noflush(struct page *page);
>> int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid);
>> +int folio_zap_direct_map(struct folio *folio);
>> +int folio_restore_direct_map(struct folio *folio);
>> bool kernel_page_present(struct page *page);
>>
>> int set_memory_encrypted(unsigned long addr, int numpages);
>> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c
>> index f0e784b963e6..a94eff324dda 100644
>> --- a/arch/arm64/mm/pageattr.c
>> +++ b/arch/arm64/mm/pageattr.c
>> @@ -357,6 +357,18 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)
>> return set_memory_valid(addr, nr, valid);
>> }
>>
>> +int folio_zap_direct_map(struct folio *folio)
>> +{
>> + return set_direct_map_valid_noflush(folio_page(folio, 0),
>> + folio_nr_pages(folio), false);
>> +}
>> +
>> +int folio_restore_direct_map(struct folio *folio)
>> +{
>> + return set_direct_map_valid_noflush(folio_page(folio, 0),
>> + folio_nr_pages(folio), true);
>> +}
>> +
>> #ifdef CONFIG_DEBUG_PAGEALLOC
>> /*
>> * This is - apart from the return value - doing the same
>> diff --git a/arch/loongarch/include/asm/set_memory.h b/arch/loongarch/include/asm/set_memory.h
>> index 55dfaefd02c8..9bc80ac420a9 100644
>> --- a/arch/loongarch/include/asm/set_memory.h
>> +++ b/arch/loongarch/include/asm/set_memory.h
>> @@ -18,5 +18,7 @@ bool kernel_page_present(struct page *page);
>> int set_direct_map_default_noflush(struct page *page);
>> int set_direct_map_invalid_noflush(struct page *page);
>> int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid);
>> +int folio_zap_direct_map(struct folio *folio);
>> +int folio_restore_direct_map(struct folio *folio);
>>
>> #endif /* _ASM_LOONGARCH_SET_MEMORY_H */
>> diff --git a/arch/loongarch/mm/pageattr.c b/arch/loongarch/mm/pageattr.c
>> index f5e910b68229..14bd322dd112 100644
>> --- a/arch/loongarch/mm/pageattr.c
>> +++ b/arch/loongarch/mm/pageattr.c
>> @@ -236,3 +236,19 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)
>>
>> return __set_memory(addr, 1, set, clear);
>> }
>> +
>> +int folio_zap_direct_map(struct folio *folio)
>> +{
>> + int ret;
>> +
>> + ret = set_direct_map_valid_noflush(folio_page(folio, 0),
>> + folio_nr_pages(folio), false);
>> +
>> + return ret;
> Why not use a single statement which is the same as the ARM64 version?
> The RISCV version has the same problem.
No reason for them to be different. Will update in the next version.
Thank you!
>
> Huacai
>
>> +}
>> +
>> +int folio_restore_direct_map(struct folio *folio)
>> +{
>> + return set_direct_map_valid_noflush(folio_page(folio, 0),
>> + folio_nr_pages(folio), true);
>> +}
>> diff --git a/arch/riscv/include/asm/set_memory.h b/arch/riscv/include/asm/set_memory.h
>> index 87389e93325a..16557b70c830 100644
>> --- a/arch/riscv/include/asm/set_memory.h
>> +++ b/arch/riscv/include/asm/set_memory.h
>> @@ -43,6 +43,8 @@ static inline int set_kernel_memory(char *startp, char *endp,
>> int set_direct_map_invalid_noflush(struct page *page);
>> int set_direct_map_default_noflush(struct page *page);
>> int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid);
>> +int folio_zap_direct_map(struct folio *folio);
>> +int folio_restore_direct_map(struct folio *folio);
>> bool kernel_page_present(struct page *page);
>>
>> #endif /* __ASSEMBLER__ */
>> diff --git a/arch/riscv/mm/pageattr.c b/arch/riscv/mm/pageattr.c
>> index 3f76db3d2769..2c218868114b 100644
>> --- a/arch/riscv/mm/pageattr.c
>> +++ b/arch/riscv/mm/pageattr.c
>> @@ -401,6 +401,22 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)
>> return __set_memory((unsigned long)page_address(page), nr, set, clear);
>> }
>>
>> +int folio_zap_direct_map(struct folio *folio)
>> +{
>> + int ret;
>> +
>> + ret = set_direct_map_valid_noflush(folio_page(folio, 0),
>> + folio_nr_pages(folio), false);
>> +
>> + return ret;
>> +}
>> +
>> +int folio_restore_direct_map(struct folio *folio)
>> +{
>> + return set_direct_map_valid_noflush(folio_page(folio, 0),
>> + folio_nr_pages(folio), true);
>> +}
>> +
>> #ifdef CONFIG_DEBUG_PAGEALLOC
>> static int debug_pagealloc_set_page(pte_t *pte, unsigned long addr, void *data)
>> {
>> diff --git a/arch/s390/include/asm/set_memory.h b/arch/s390/include/asm/set_memory.h
>> index 94092f4ae764..fc73652e5715 100644
>> --- a/arch/s390/include/asm/set_memory.h
>> +++ b/arch/s390/include/asm/set_memory.h
>> @@ -63,6 +63,8 @@ __SET_MEMORY_FUNC(set_memory_4k, SET_MEMORY_4K)
>> int set_direct_map_invalid_noflush(struct page *page);
>> int set_direct_map_default_noflush(struct page *page);
>> int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid);
>> +int folio_zap_direct_map(struct folio *folio);
>> +int folio_restore_direct_map(struct folio *folio);
>> bool kernel_page_present(struct page *page);
>>
>> #endif
>> diff --git a/arch/s390/mm/pageattr.c b/arch/s390/mm/pageattr.c
>> index d3ce04a4b248..df4a487b484d 100644
>> --- a/arch/s390/mm/pageattr.c
>> +++ b/arch/s390/mm/pageattr.c
>> @@ -412,6 +412,24 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)
>> return __set_memory((unsigned long)page_to_virt(page), nr, flags);
>> }
>>
>> +int folio_zap_direct_map(struct folio *folio)
>> +{
>> + unsigned long addr = (unsigned long)folio_address(folio);
>> + int ret;
>> +
>> + ret = set_direct_map_valid_noflush(folio_page(folio, 0),
>> + folio_nr_pages(folio), false);
>> + flush_tlb_kernel_range(addr, addr + folio_size(folio));
>> +
>> + return ret;
>> +}
>> +
>> +int folio_restore_direct_map(struct folio *folio)
>> +{
>> + return set_direct_map_valid_noflush(folio_page(folio, 0),
>> + folio_nr_pages(folio), true);
>> +}
>> +
>> bool kernel_page_present(struct page *page)
>> {
>> unsigned long addr;
>> diff --git a/arch/x86/include/asm/set_memory.h b/arch/x86/include/asm/set_memory.h
>> index 61f56cdaccb5..7208af609121 100644
>> --- a/arch/x86/include/asm/set_memory.h
>> +++ b/arch/x86/include/asm/set_memory.h
>> @@ -90,6 +90,8 @@ int set_pages_rw(struct page *page, int numpages);
>> int set_direct_map_invalid_noflush(struct page *page);
>> int set_direct_map_default_noflush(struct page *page);
>> int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid);
>> +int folio_zap_direct_map(struct folio *folio);
>> +int folio_restore_direct_map(struct folio *folio);
>> bool kernel_page_present(struct page *page);
>>
>> extern int kernel_set_to_readonly;
>> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
>> index 6c6eb486f7a6..3f0fc30eb320 100644
>> --- a/arch/x86/mm/pat/set_memory.c
>> +++ b/arch/x86/mm/pat/set_memory.c
>> @@ -2656,6 +2656,26 @@ int set_direct_map_valid_noflush(struct page *page, unsigned nr, bool valid)
>> return __set_pages_np(page, nr);
>> }
>>
>> +int folio_zap_direct_map(struct folio *folio)
>> +{
>> + unsigned long addr = (unsigned long)folio_address(folio);
>> + int ret;
>> +
>> + ret = set_direct_map_valid_noflush(folio_page(folio, 0),
>> + folio_nr_pages(folio), false);
>> + flush_tlb_kernel_range(addr, addr + folio_size(folio));
>> +
>> + return ret;
>> +}
>> +EXPORT_SYMBOL_FOR_MODULES(folio_zap_direct_map, "kvm");
>> +
>> +int folio_restore_direct_map(struct folio *folio)
>> +{
>> + return set_direct_map_valid_noflush(folio_page(folio, 0),
>> + folio_nr_pages(folio), true);
>> +}
>> +EXPORT_SYMBOL_FOR_MODULES(folio_restore_direct_map, "kvm");
>> +
>> #ifdef CONFIG_DEBUG_PAGEALLOC
>> void __kernel_map_pages(struct page *page, int numpages, int enable)
>> {
>> diff --git a/include/linux/set_memory.h b/include/linux/set_memory.h
>> index 3030d9245f5a..8d1c8a7f7d79 100644
>> --- a/include/linux/set_memory.h
>> +++ b/include/linux/set_memory.h
>> @@ -40,6 +40,16 @@ static inline int set_direct_map_valid_noflush(struct page *page,
>> return 0;
>> }
>>
>> +static inline int folio_zap_direct_map(struct folio *folio)
>> +{
>> + return 0;
>> +}
>> +
>> +static inline int folio_restore_direct_map(struct folio *folio)
>> +{
>> + return 0;
>> +}
>> +
>> static inline bool kernel_page_present(struct page *page)
>> {
>> return true;
>> --
>> 2.50.1
>>
>>
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