mm: Add fault_in_subpage_writeable() to probe at sub-page granularity

On hardware with features like arm64 MTE or SPARC ADI, an access fault
can be triggered at sub-page granularity. Depending on how the
fault_in_writeable() function is used, the caller can get into a
live-lock by continuously retrying the fault-in on an address different
from the one where the uaccess failed.

In the majority of cases progress is ensured by the following
conditions:

1. copy_to_user_nofault() guarantees at least one byte access if the
   user address is not faulting.

2. The fault_in_writeable() loop is resumed from the first address that
   could not be accessed by copy_to_user_nofault().

If the loop iteration is restarted from an earlier (initial) point, the
loop is repeated with the same conditions and it would live-lock.

Introduce an arch-specific probe_subpage_writeable() and call it from
the newly added fault_in_subpage_writeable() function. The arch code
with sub-page faults will have to implement the specific probing
functionality.

Note that no other fault_in_subpage_*() functions are added since they
have no callers currently susceptible to a live-lock.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: https://lore.kernel.org/r/20220423100751.1870771-2-catalin.marinas@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Catalin Marinas
2022-04-23 11:07:49 +01:00
parent b2d229d4dd
commit da32b58172
4 changed files with 59 additions and 0 deletions

View File

@@ -231,6 +231,28 @@ static inline bool pagefault_disabled(void)
*/
#define faulthandler_disabled() (pagefault_disabled() || in_atomic())
#ifndef CONFIG_ARCH_HAS_SUBPAGE_FAULTS
/**
* probe_subpage_writeable: probe the user range for write faults at sub-page
* granularity (e.g. arm64 MTE)
* @uaddr: start of address range
* @size: size of address range
*
* Returns 0 on success, the number of bytes not probed on fault.
*
* It is expected that the caller checked for the write permission of each
* page in the range either by put_user() or GUP. The architecture port can
* implement a more efficient get_user() probing if the same sub-page faults
* are triggered by either a read or a write.
*/
static inline size_t probe_subpage_writeable(char __user *uaddr, size_t size)
{
return 0;
}
#endif /* CONFIG_ARCH_HAS_SUBPAGE_FAULTS */
#ifndef ARCH_HAS_NOCACHE_UACCESS
static inline __must_check unsigned long