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66dbd6e61a
When hardware updates of the access and dirty states are enabled, the
default ptep_set_access_flags() implementation based on calling
set_pte_at() directly is potentially racy. This triggers the "racy dirty
state clearing" warning in set_pte_at() because an existing writable PTE
is overridden with a clean entry.
There are two main scenarios for this situation:
1. The CPU getting an access fault does not support hardware updates of
the access/dirty flags. However, a different agent in the system
(e.g. SMMU) can do this, therefore overriding a writable entry with a
clean one could potentially lose the automatically updated dirty
status
2. A more complex situation is possible when all CPUs support hardware
AF/DBM:
a) Initial state: shareable + writable vma and pte_none(pte)
b) Read fault taken by two threads of the same process on different
CPUs
c) CPU0 takes the mmap_sem and proceeds to handling the fault. It
eventually reaches do_set_pte() which sets a writable + clean pte.
CPU0 releases the mmap_sem
d) CPU1 acquires the mmap_sem and proceeds to handle_pte_fault(). The
pte entry it reads is present, writable and clean and it continues
to pte_mkyoung()
e) CPU1 calls ptep_set_access_flags()
If between (d) and (e) the hardware (another CPU) updates the dirty
state (clears PTE_RDONLY), CPU1 will override the PTR_RDONLY bit
marking the entry clean again.
This patch implements an arm64-specific ptep_set_access_flags() function
to perform an atomic update of the PTE flags.
Fixes:
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|---|---|---|
| .. | ||
| alpha | ||
| arc | ||
| arm | ||
| arm64 | ||
| avr32 | ||
| blackfin | ||
| c6x | ||
| cris | ||
| frv | ||
| h8300 | ||
| hexagon | ||
| ia64 | ||
| m32r | ||
| m68k | ||
| metag | ||
| microblaze | ||
| mips | ||
| mn10300 | ||
| nios2 | ||
| openrisc | ||
| parisc | ||
| powerpc | ||
| s390 | ||
| score | ||
| sh | ||
| sparc | ||
| tile | ||
| um | ||
| unicore32 | ||
| x86 | ||
| xtensa | ||
| .gitignore | ||
| Kconfig | ||