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Message-ID: <CAAhV-H6S4bVdpwbER84-iwSE+bQrFu_gF=Ww-bCFxThJ7WiUwQ@mail.gmail.com>
Date: Thu, 15 Jan 2026 18:54:27 +0800
From: Huacai Chen <chenhuacai@...nel.org>
To: "Kalyazin, Nikita" <kalyazin@...zon.co.uk>
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Subject: Re: [PATCH v9 01/13] set_memory: add folio_{zap,restore}_direct_map helpers
Hi, Nikita,
On Wed, Jan 14, 2026 at 9:45 PM Kalyazin, Nikita <kalyazin@...zon.co.uk> wrote:
>
> From: Nikita Kalyazin <kalyazin@...zon.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@...zon.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.
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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