Messages in this thread | | | Subject | Re: [PATCH 2/4] arm64/mm: wire up CONFIG_ARCH_HAS_SET_DIRECT_MAP | From | Ard Biesheuvel <> | Date | Tue, 28 May 2019 10:20:46 +0200 |
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On 5/28/19 10:10 AM, Anshuman Khandual wrote: > > > On 05/23/2019 03:52 PM, Ard Biesheuvel wrote: >> Wire up the special helper functions to manipulate aliases of vmalloc >> regions in the linear map. > > IMHO the commit message here could be bit more descriptive because of the > amount of changes this patch brings in. > >> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@arm.com> >> --- >> arch/arm64/Kconfig | 1 + >> arch/arm64/include/asm/cacheflush.h | 3 ++ >> arch/arm64/mm/pageattr.c | 48 ++++++++++++++++---- >> mm/vmalloc.c | 11 ----- >> 4 files changed, 44 insertions(+), 19 deletions(-) >> >> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig >> index ca9c175fb949..4ab32180eabd 100644 >> --- a/arch/arm64/Kconfig >> +++ b/arch/arm64/Kconfig >> @@ -26,6 +26,7 @@ config ARM64 >> select ARCH_HAS_MEMBARRIER_SYNC_CORE >> select ARCH_HAS_PTE_SPECIAL >> select ARCH_HAS_SETUP_DMA_OPS >> + select ARCH_HAS_SET_DIRECT_MAP >> select ARCH_HAS_SET_MEMORY >> select ARCH_HAS_STRICT_KERNEL_RWX >> select ARCH_HAS_STRICT_MODULE_RWX >> diff --git a/arch/arm64/include/asm/cacheflush.h b/arch/arm64/include/asm/cacheflush.h >> index 19844211a4e6..b9ee5510067f 100644 >> --- a/arch/arm64/include/asm/cacheflush.h >> +++ b/arch/arm64/include/asm/cacheflush.h >> @@ -187,4 +187,7 @@ static inline void flush_cache_vunmap(unsigned long start, unsigned long end) >> >> 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); >> + >> #endif >> diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c >> index 6cd645edcf35..9c6b9039ec8f 100644 >> --- a/arch/arm64/mm/pageattr.c >> +++ b/arch/arm64/mm/pageattr.c >> @@ -159,17 +159,48 @@ int set_memory_valid(unsigned long addr, int numpages, int enable) >> __pgprot(PTE_VALID)); >> } >> >> -#ifdef CONFIG_DEBUG_PAGEALLOC >> +int set_direct_map_invalid_noflush(struct page *page) >> +{ >> + struct page_change_data data = { >> + .set_mask = __pgprot(0), >> + .clear_mask = __pgprot(PTE_VALID), >> + }; >> + >> + if (!rodata_full) >> + return 0; > > Why rodata_full needs to be probed here ? Should not we still require the following > transition even if rodata_full is not enabled. Just wondering whether we can use > VM_FLUSH_RESET_PERMS feature without these required transitions. > > /* > * Set direct map to something invalid so that it won't be cached if > * there are any accesses after the TLB flush, then flush the TLB and > * reset the direct map permissions to the default. > */ > set_area_direct_map(area, set_direct_map_invalid_noflush); > _vm_unmap_aliases(start, end, 1); > set_area_direct_map(area, set_direct_map_default_noflush); > > > +
How would that work? With rodata_full disabled, the linear region is not mapped down to pages, and so there is no way we can manipulate linear aliases at page granularity.
>> + return apply_to_page_range(&init_mm, >> + (unsigned long)page_address(page), >> + PAGE_SIZE, change_page_range, &data); >> +} >> + >> +int set_direct_map_default_noflush(struct page *page) >> +{ >> + struct page_change_data data = { >> + .set_mask = __pgprot(PTE_VALID | PTE_WRITE), >> + .clear_mask = __pgprot(PTE_RDONLY), > > Replace __pgprot(PTE_VALID | PTE_WRITE) with PAGE_KERNEL instead ! >
This is a delta mask, so no need to pull in the PTE_MAYBE_NG or other attributes that we know we haven't changed.
>> + }; >> + >> + if (!rodata_full) >> + return 0; >> + >> + return apply_to_page_range(&init_mm, >> + (unsigned long)page_address(page), >> + PAGE_SIZE, change_page_range, &data); >> +} >> + > > IIUC set_direct_map_invalid_noflush() and set_direct_map_default_noflush() > should set *appropriate* permissions as seen fit from platform perspective > to implement this transition. > > In here set_direct_map_invalid_noflush() makes the entry invalid preventing > further MMU walks (hence new TLB entries). set_direct_map_default_noflush() > makes it a valid write entry. Though it looks similar to PAGE_KERNEL which > is the default permission for linear mapping on arm64 via __map_memblock(). > Should not PAGE_KERNEL be used explicitly as suggested above. >
No. We should restore the attributes that we cleared when manipulating the linear aliases. There isn't a lot of code that does that, so I don't see the need to use PAGE_KERNEL here.
>> void __kernel_map_pages(struct page *page, int numpages, int enable) >> { >> + if (!debug_pagealloc_enabled() && !rodata_full) >> + return; >> + > > I guess this is not related to CONFIG_ARCH_HAS_SET_DIRECT_MAP here and should > be a fix or an enhancement to CONFIG_DEBUG_PAGEALLOC implementation. Just > curious, !rodata_full check here to ensure that linear mapping does not have > block or contig mappings and should be backed by regular pages only ? >
It is related. CONFIG_ARCH_HAS_SET_DIRECT_MAP introduces references to __kernel_map_pages() in generic code, so enabling CONFIG_ARCH_HAS_SET_DIRECT_MAP should make __kernel_map_pages() available unconditionally as well.
>> set_memory_valid((unsigned long)page_address(page), numpages, enable); >> } >> -#ifdef CONFIG_HIBERNATION >> + >> /* >> - * When built with CONFIG_DEBUG_PAGEALLOC and CONFIG_HIBERNATION, this function >> - * is used to determine if a linear map page has been marked as not-valid by >> - * CONFIG_DEBUG_PAGEALLOC. Walk the page table and check the PTE_VALID bit. >> - * This is based on kern_addr_valid(), which almost does what we need. >> + * This function is used to determine if a linear map page has been marked as >> + * not-valid. Walk the page table and check the PTE_VALID bit. This is based >> + * on kern_addr_valid(), which almost does what we need. >> * >> * Because this is only called on the kernel linear map, p?d_sect() implies >> * p?d_present(). When debug_pagealloc is enabled, sections mappings are >> @@ -183,6 +214,9 @@ bool kernel_page_present(struct page *page) >> pte_t *ptep; >> unsigned long addr = (unsigned long)page_address(page); >> >> + if (!debug_pagealloc_enabled() && !rodata_full) >> + return true; >> + > > Ditto, not related to CONFIG_ARCH_HAS_SET_DIRECT_MAP. >
It is related.
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