From: Ard Biesheuvel ardb@kernel.org Subject: kmap_local: don't assume kmap PTEs are linear arrays in memory

The kmap_local conversion broke the ARM architecture, because the new code assumes that all PTEs used for creating kmaps form a linear array in memory, and uses array indexing to look up the kmap PTE belonging to a certain kmap index.

On ARM, this cannot work, not only because the PTE pages may be non-adjacent in memory, but also because ARM/!LPAE interleaves hardware entries and extended entries (carrying software-only bits) in a way that is not compatible with array indexing.

Fortunately, this only seems to affect configurations with more than 8 CPUs, due to the way the per-CPU kmap slots are organized in memory.

Work around this by permitting an architecture to set a Kconfig symbol that signifies that the kmap PTEs do not form a lineary array in memory, and so the only way to locate the appropriate one is to walk the page tables.

Link: https://lore.kernel.org/linux-arm-kernel/20211026131249.3731275-1-ardb@kerne... Link: https://lkml.kernel.org/r/20211116094737.7391-1-ardb@kernel.org Fixes: 2a15ba82fa6c ("ARM: highmem: Switch to generic kmap atomic") Signed-off-by: Ard Biesheuvel ardb@kernel.org Reported-by: Quanyang Wang quanyang.wang@windriver.com Reviewed-by: Linus Walleij linus.walleij@linaro.org Acked-by: Russell King (Oracle) rmk+kernel@armlinux.org.uk Cc: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

arch/arm/Kconfig | 1 + mm/Kconfig | 3 +++ mm/highmem.c | 32 +++++++++++++++++++++----------- 3 files changed, 25 insertions(+), 11 deletions(-)

--- a/arch/arm/Kconfig~kmap_local-dont-assume-kmap-ptes-are-linear-arrays-in-memory +++ a/arch/arm/Kconfig @@ -1463,6 +1463,7 @@ config HIGHMEM bool "High Memory Support" depends on MMU select KMAP_LOCAL + select KMAP_LOCAL_NON_LINEAR_PTE_ARRAY help The address space of ARM processors is only 4 Gigabytes large and it has to accommodate user address space, kernel address --- a/mm/highmem.c~kmap_local-dont-assume-kmap-ptes-are-linear-arrays-in-memory +++ a/mm/highmem.c @@ -503,16 +503,22 @@ static inline int kmap_local_calc_idx(in

static pte_t *__kmap_pte;

-static pte_t *kmap_get_pte(void) +static pte_t *kmap_get_pte(unsigned long vaddr, int idx) { + if (IS_ENABLED(CONFIG_KMAP_LOCAL_NON_LINEAR_PTE_ARRAY)) + /* + * Set by the arch if __kmap_pte[-idx] does not produce + * the correct entry. + */ + return virt_to_kpte(vaddr); if (!__kmap_pte) __kmap_pte = virt_to_kpte(__fix_to_virt(FIX_KMAP_BEGIN)); - return __kmap_pte; + return &__kmap_pte[-idx]; }

void *__kmap_local_pfn_prot(unsigned long pfn, pgprot_t prot) { - pte_t pteval, *kmap_pte = kmap_get_pte(); + pte_t pteval, *kmap_pte; unsigned long vaddr; int idx;

@@ -524,9 +530,10 @@ void *__kmap_local_pfn_prot(unsigned lon preempt_disable(); idx = arch_kmap_local_map_idx(kmap_local_idx_push(), pfn); vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx); - BUG_ON(!pte_none(*(kmap_pte - idx))); + kmap_pte = kmap_get_pte(vaddr, idx); + BUG_ON(!pte_none(*kmap_pte)); pteval = pfn_pte(pfn, prot); - arch_kmap_local_set_pte(&init_mm, vaddr, kmap_pte - idx, pteval); + arch_kmap_local_set_pte(&init_mm, vaddr, kmap_pte, pteval); arch_kmap_local_post_map(vaddr, pteval); current->kmap_ctrl.pteval[kmap_local_idx()] = pteval; preempt_enable(); @@ -559,7 +566,7 @@ EXPORT_SYMBOL(__kmap_local_page_prot); void kunmap_local_indexed(void *vaddr) { unsigned long addr = (unsigned long) vaddr & PAGE_MASK; - pte_t *kmap_pte = kmap_get_pte(); + pte_t *kmap_pte; int idx;

if (addr < __fix_to_virt(FIX_KMAP_END) || @@ -584,8 +591,9 @@ void kunmap_local_indexed(void *vaddr) idx = arch_kmap_local_unmap_idx(kmap_local_idx(), addr); WARN_ON_ONCE(addr != __fix_to_virt(FIX_KMAP_BEGIN + idx));

+ kmap_pte = kmap_get_pte(addr, idx); arch_kmap_local_pre_unmap(addr); - pte_clear(&init_mm, addr, kmap_pte - idx); + pte_clear(&init_mm, addr, kmap_pte); arch_kmap_local_post_unmap(addr); current->kmap_ctrl.pteval[kmap_local_idx()] = __pte(0); kmap_local_idx_pop(); @@ -607,7 +615,7 @@ EXPORT_SYMBOL(kunmap_local_indexed); void __kmap_local_sched_out(void) { struct task_struct *tsk = current; - pte_t *kmap_pte = kmap_get_pte(); + pte_t *kmap_pte; int i;

/* Clear kmaps */ @@ -634,8 +642,9 @@ void __kmap_local_sched_out(void) idx = arch_kmap_local_map_idx(i, pte_pfn(pteval));

addr = __fix_to_virt(FIX_KMAP_BEGIN + idx); + kmap_pte = kmap_get_pte(addr, idx); arch_kmap_local_pre_unmap(addr); - pte_clear(&init_mm, addr, kmap_pte - idx); + pte_clear(&init_mm, addr, kmap_pte); arch_kmap_local_post_unmap(addr); } } @@ -643,7 +652,7 @@ void __kmap_local_sched_out(void) void __kmap_local_sched_in(void) { struct task_struct *tsk = current; - pte_t *kmap_pte = kmap_get_pte(); + pte_t *kmap_pte; int i;

/* Restore kmaps */ @@ -663,7 +672,8 @@ void __kmap_local_sched_in(void) /* See comment in __kmap_local_sched_out() */ idx = arch_kmap_local_map_idx(i, pte_pfn(pteval)); addr = __fix_to_virt(FIX_KMAP_BEGIN + idx); - set_pte_at(&init_mm, addr, kmap_pte - idx, pteval); + kmap_pte = kmap_get_pte(addr, idx); + set_pte_at(&init_mm, addr, kmap_pte, pteval); arch_kmap_local_post_map(addr, pteval); } } --- a/mm/Kconfig~kmap_local-dont-assume-kmap-ptes-are-linear-arrays-in-memory +++ a/mm/Kconfig @@ -890,6 +890,9 @@ config MAPPING_DIRTY_HELPERS config KMAP_LOCAL bool

+config KMAP_LOCAL_NON_LINEAR_PTE_ARRAY + bool + # struct io_mapping based helper. Selected by drivers that need them config IO_MAPPING bool _