[PATCH 5.15 198/279] kmap_local: dont assume kmap PTEs are linear arrays in memory

Greg Kroah-Hartman
2021-11-24T14:03:38Z

From: Ard Biesheuvel <ardb@kernel.org>

commit 825c43f50e3aa811a291ffcb40e02fbf6d91ba86 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm/Kconfig | 1 +
mm/Kconfig | 3 +++
mm/highmem.c | 32 +++++++++++++++++++++-----------
3 files changed, 25 insertions(+), 11 deletions(-)

--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1455,6 +1455,7 @@ 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/Kconfig
+++ b/mm/Kconfig
@@ -887,6 +887,9 @@ 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
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -504,16 +504,22 @@ 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;

@@ -525,9 +531,10 @@ 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();
@@ -560,7 +567,7 @@ 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) ||
@@ -585,8 +592,9 @@ 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();
@@ -608,7 +616,7 @@ 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 */
@@ -635,8 +643,9 @@ 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);
}
}
@@ -644,7 +653,7 @@ 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 */
@@ -664,7 +673,8 @@ 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);
}
}