| Message ID | 20221006040555.1502679-1-ira.weiny@intel.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [V2] highmem: Fix kmap_to_page() for kmap_local_page() addresses | expand |
On Wed, 5 Oct 2022 21:05:55 -0700 ira.weiny@intel.com wrote: > kmap_to_page() is used to get the page for a virtual address which may > be kmap'ed. Unfortunately, kmap_local_page() stores mappings in a > thread local array separate from kmap(). These mappings were not > checked by the call. > > Check the kmap_local_page() mappings and return the page if found. > > Because it is intended to remove kmap_to_page() add a warn on once to > the kmap checks to flag potential issues early. What were the user-visible runtime effects of this? Are we able to identify a Fixes:? Thanks.
On Thu, Oct 06, 2022 at 01:33:31PM -0700, Andrew Morton wrote: > On Wed, 5 Oct 2022 21:05:55 -0700 ira.weiny@intel.com wrote: > > > kmap_to_page() is used to get the page for a virtual address which may > > be kmap'ed. Unfortunately, kmap_local_page() stores mappings in a > > thread local array separate from kmap(). These mappings were not > > checked by the call. > > > > Check the kmap_local_page() mappings and return the page if found. > > > > Because it is intended to remove kmap_to_page() add a warn on once to > > the kmap checks to flag potential issues early. > > What were the user-visible runtime effects of this? No one actually hit a bug with this because AFAIK only one kmap() call has been converted to kmap_local_page() which then eventually calls kmap_to_page(). https://lore.kernel.org/lkml/YzN+ZYLjK6HI1P1C@ZenIV/ However that has already been fixed by Al in that thread. > > Are we able to identify a Fixes:? I suppose this could be added as a Fixes: to the original patch introducing kmap_local_page()? But one could argue that kmap_to_page() was only intended to support kmap() addresses because it does not work with kmap_atomic() addresses either. I'm proposing this as a stop gap to ensure that work can continue on converting kmap() uses to kmap_local_page() without fear of causing breakage while simultaneously we evaluate and hopefully remove kmap_to_page() as well. Ira
diff --git a/mm/highmem.c b/mm/highmem.c index c707d7202d5f..529987b28205 100644 --- a/mm/highmem.c +++ b/mm/highmem.c @@ -30,6 +30,17 @@ #include <asm/tlbflush.h> #include <linux/vmalloc.h> +#ifdef CONFIG_KMAP_LOCAL +static inline int kmap_local_calc_idx(int idx) +{ + return idx + KM_MAX_IDX * smp_processor_id(); +} + +#ifndef arch_kmap_local_map_idx +#define arch_kmap_local_map_idx(idx, pfn) kmap_local_calc_idx(idx) +#endif +#endif /* CONFIG_KMAP_LOCAL */ + /* * Virtual_count is not a pure "count". * 0 means that it is not mapped, and has not been mapped @@ -142,14 +153,34 @@ pte_t *pkmap_page_table; struct page *__kmap_to_page(void *vaddr) { + unsigned long base = (unsigned long) vaddr & PAGE_MASK; + struct kmap_ctrl *kctrl = ¤t->kmap_ctrl; unsigned long addr = (unsigned long)vaddr; + int i; - if (addr >= PKMAP_ADDR(0) && addr < PKMAP_ADDR(LAST_PKMAP)) { + /* kmap() mappings */ + if (WARN_ON_ONCE(addr >= PKMAP_ADDR(0) && + addr < PKMAP_ADDR(LAST_PKMAP))) { int i = PKMAP_NR(addr); return pte_page(pkmap_page_table[i]); } + /* kmap_local_page() mappings */ + if (WARN_ON_ONCE(base >= __fix_to_virt(FIX_KMAP_END) && + base < __fix_to_virt(FIX_KMAP_BEGIN))) { + for (i = 0; i < kctrl->idx; i++) { + unsigned long base_addr; + int idx; + + idx = arch_kmap_local_map_idx(i, pte_pfn(pteval)); + base_addr = __fix_to_virt(FIX_KMAP_BEGIN + idx); + + if (base_addr == base) + return pte_page(kctrl->pteval[i]); + } + } + return virt_to_page(vaddr); } EXPORT_SYMBOL(__kmap_to_page); @@ -462,10 +493,6 @@ static inline void kmap_local_idx_pop(void) # define arch_kmap_local_post_unmap(vaddr) do { } while (0) #endif -#ifndef arch_kmap_local_map_idx -#define arch_kmap_local_map_idx(idx, pfn) kmap_local_calc_idx(idx) -#endif - #ifndef arch_kmap_local_unmap_idx #define arch_kmap_local_unmap_idx(idx, vaddr) kmap_local_calc_idx(idx) #endif @@ -494,11 +521,6 @@ static inline bool kmap_high_unmap_local(unsigned long vaddr) return false; } -static inline int kmap_local_calc_idx(int idx) -{ - return idx + KM_MAX_IDX * smp_processor_id(); -} - static pte_t *__kmap_pte; static pte_t *kmap_get_pte(unsigned long vaddr, int idx)