Re: [PATCH v3 0/9] Fixup page directory freeing

Aneesh Kumar K.V
2020-01-14T12:29:14Z

On 1/14/20 4:20 PM, Peter Zijlstra wrote:
> On Tue, Jan 14, 2020 at 03:31:36PM +0530, Aneesh Kumar K.V wrote:
>> This is a repost of patch series from Peter with the arch specific changes except ppc64 dropped.
>> ppc64 changes are added here because we are redoing the patch series on top of ppc64 changes. This makes it
>> easy to backport these changes. Only the first 3 patches need to be backported to stable.
>>
>> The thing is, on anything SMP, freeing page directories should observe the
>> exact same order as normal page freeing:
>>
>> 1) unhook page/directory
>> 2) TLB invalidate
>> 3) free page/directory
>>
>> Without this, any concurrent page-table walk could end up with a Use-after-Free.
>> This is esp. trivial for anything that has software page-table walkers
>> (HAVE_FAST_GUP / software TLB fill) or the hardware caches partial page-walks
>> (ie. caches page directories).
>>
>> Even on UP this might give issues since mmu_gather is preemptible these days.
>> An interrupt or preempted task accessing user pages might stumble into the free
>> page if the hardware caches page directories.
>>
>> This patch series fixup ppc64 and add generic MMU_GATHER changes to support the conversion of other architectures.
>> I haven't added patches w.r.t other architecture because they are yet to be acked.
>
> Obviously looks good to me; will you route this through the Power tree
> since you're in a hurry to see this fixed?
>

Michael,

Can you take this via your tree?

-aneesh