[PATCH v4 0/4] arm64/mm: Enable userfaultfd write-protect

[Ryan Roberts]

On 07/05/2024 12:07, Will Deacon wrote:
> Hi Ryan,
> 
> On Fri, May 03, 2024 at 03:45:58PM +0100, Ryan Roberts wrote:
>> This series adds uffd write-protect support for arm64.
>>
>> Previous attempts to add uffd-wp (and soft-dirty) have failed because of a
>> perceived lack of available PTE SW bits. However it actually turns out that
>> there are 2 available but they are hidden. PTE_PROT_NONE was previously
>> occupying a SW bit, but can be moved, freeing up the SW bit. Bit 63 is marked as
>> "IGNORED" in the Arm ARM, but it does not currently indicate "reserved for SW
>> use" like it does for the other SW bits. I've confirmed with the spec owner that
>> this is an oversight; the bit is intended to be reserved for SW use and the spec
>> will clarify this in a future update.
>>
>> So now we have two spare bits; patch 4 enables uffd-wp on arm64, using the SW
>> bit freed up by moving PTE_PROT_NONE. This leaves bit 63 spare for future use
>> (e.g. soft-dirty - see RFC at [4] - or some other usage).
>>
>> ---
>>
>> This applies on top of v6.9-rc5.
> 
> I chucked this into the CI on Friday and it looks to have survived the
> long weekend, so I've gone ahead and merged it into for-next/core. Short
> of any last minute failures (touch wood), this should land in 6.10.

Oh great - thanks!

Catalin was previously proposing to hold this until 6.11 - I'll leave you two to
fight it out in case that's still his preference ;-)

> 
> Thanks!
> 
> Will