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| author | Michael Ellerman <mpe@ellerman.id.au> | 2022-02-23 12:58:21 +1100 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2022-03-08 00:04:57 +1100 |
| commit | 591b4b268435f00d2f0b81f786c2c7bd5ef66416 (patch) | |
| tree | 8904972d059700e3bc79eb2861b46615d54df765 | |
| parent | d4679ac8ea2e5078704aa1c026db36580cc1bf9a (diff) | |
| download | linux-591b4b268435f00d2f0b81f786c2c7bd5ef66416.tar.bz2 | |
powerpc/code-patching: Pre-map patch area
Paul reported a warning with DEBUG_ATOMIC_SLEEP=y:
BUG: sleeping function called from invalid context at include/linux/sched/mm.h:256
in_atomic(): 0, irqs_disabled(): 1, non_block: 0, pid: 1, name: swapper/0
preempt_count: 0, expected: 0
...
Call Trace:
dump_stack_lvl+0xa0/0xec (unreliable)
__might_resched+0x2f4/0x310
kmem_cache_alloc+0x220/0x4b0
__pud_alloc+0x74/0x1d0
hash__map_kernel_page+0x2cc/0x390
do_patch_instruction+0x134/0x4a0
arch_jump_label_transform+0x64/0x78
__jump_label_update+0x148/0x180
static_key_enable_cpuslocked+0xd0/0x120
static_key_enable+0x30/0x50
check_kvm_guest+0x60/0x88
pSeries_smp_probe+0x54/0xb0
smp_prepare_cpus+0x3e0/0x430
kernel_init_freeable+0x20c/0x43c
kernel_init+0x30/0x1a0
ret_from_kernel_thread+0x5c/0x64
Peter pointed out that this is because do_patch_instruction() has
disabled interrupts, but then map_patch_area() calls map_kernel_page()
then hash__map_kernel_page() which does a sleeping memory allocation.
We only see the warning in KVM guests with SMT enabled, which is not
particularly common, or on other platforms if CONFIG_KPROBES is
disabled, also not common. The reason we don't see it in most
configurations is that another path that happens to have interrupts
enabled has allocated the required page tables for us, eg. there's a
path in kprobes init that does that. That's just pure luck though.
As Christophe suggested, the simplest solution is to do a dummy
map/unmap when we initialise the patching, so that any required page
table levels are pre-allocated before the first call to
do_patch_instruction(). This works because the unmap doesn't free any
page tables that were allocated by the map, it just clears the PTE,
leaving the page table levels there for the next map.
Reported-by: Paul Menzel <pmenzel@molgen.mpg.de>
Debugged-by: Peter Zijlstra <peterz@infradead.org>
Suggested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220223015821.473097-1-mpe@ellerman.id.au
| -rw-r--r-- | arch/powerpc/lib/code-patching.c | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c index 906d43463366..00c68e7fb11e 100644 --- a/arch/powerpc/lib/code-patching.c +++ b/arch/powerpc/lib/code-patching.c @@ -43,9 +43,14 @@ int raw_patch_instruction(u32 *addr, ppc_inst_t instr) #ifdef CONFIG_STRICT_KERNEL_RWX static DEFINE_PER_CPU(struct vm_struct *, text_poke_area); +static int map_patch_area(void *addr, unsigned long text_poke_addr); +static void unmap_patch_area(unsigned long addr); + static int text_area_cpu_up(unsigned int cpu) { struct vm_struct *area; + unsigned long addr; + int err; area = get_vm_area(PAGE_SIZE, VM_ALLOC); if (!area) { @@ -53,6 +58,15 @@ static int text_area_cpu_up(unsigned int cpu) cpu); return -1; } + + // Map/unmap the area to ensure all page tables are pre-allocated + addr = (unsigned long)area->addr; + err = map_patch_area(empty_zero_page, addr); + if (err) + return err; + + unmap_patch_area(addr); + this_cpu_write(text_poke_area, area); return 0; |