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@kernel.org/
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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index f0f9e8b..c2724d9 100644 (file)
--- a/arch/arm/Kconfig
+++ b/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

diff --git a/mm/Kconfig b/mm/Kconfig
index 068ce59..28edafc 100644 (file)
--- a/mm/Kconfig
+++ b/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

diff --git a/mm/highmem.c b/mm/highmem.c
index 88f65f1..ca9fa8c 100644 (file)
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -503,16 +503,22 @@ static inline int kmap_local_calc_idx(int idx)
 
 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 long pfn, pgprot_t prot)
        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);
        }
 }