The test driver uses an xa_array to store virtual to physical address
translations for a simulated hardware device. The MMU notifier
invalidation callback is used to keep the table consistent with the CPU
page table and is frequently called only for a page or two. However, if
the test process exits unexpectedly or is killed, the range can be
[0..ULONG_MAX] in which case calling xa_erase() for every possible PFN
results in CPU timeouts. Munmap() can result in a large range being
invalidated but in that case, the xa_array is likely to contain entries
that need to be invalidated.
Check for [0..ULONG_MAX] explicitly and just destroy the whole table.
Signed-off-by: Ralph Campbell <[email protected]>
---
This patch is based on Jason Gunthorpe's hmm tree and should be folded
into the ("mm/hmm/test: add selftest driver for HMM") patch once this
patch is reviewed, etc.
lib/test_hmm.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index 8b36c26b717b..b89852ec3c29 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -201,7 +201,13 @@ static void dmirror_do_update(struct dmirror *dmirror, unsigned long start,
* The XArray doesn't hold references to pages since it relies on
* the mmu notifier to clear page pointers when they become stale.
* Therefore, it is OK to just clear the entry.
+ * However, if the entire address space is being invalidated, it
+ * takes too long to clear them one at a time so destroy the array.
*/
+ if (start == 0 && end == ULONG_MAX) {
+ xa_destroy(&dmirror->pt);
+ return;
+ }
for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++)
xa_erase(&dmirror->pt, pfn);
}
--
2.20.1
On Wed, May 13, 2020 at 02:45:07PM -0700, Ralph Campbell wrote:
> The test driver uses an xa_array to store virtual to physical address
> translations for a simulated hardware device. The MMU notifier
> invalidation callback is used to keep the table consistent with the CPU
> page table and is frequently called only for a page or two. However, if
> the test process exits unexpectedly or is killed, the range can be
> [0..ULONG_MAX] in which case calling xa_erase() for every possible PFN
> results in CPU timeouts. Munmap() can result in a large range being
> invalidated but in that case, the xa_array is likely to contain entries
> that need to be invalidated.
> Check for [0..ULONG_MAX] explicitly and just destroy the whole table.
>
> Signed-off-by: Ralph Campbell <[email protected]>
>
> This patch is based on Jason Gunthorpe's hmm tree and should be folded
> into the ("mm/hmm/test: add selftest driver for HMM") patch once this
> patch is reviewed, etc.
>
> lib/test_hmm.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/lib/test_hmm.c b/lib/test_hmm.c
> index 8b36c26b717b..b89852ec3c29 100644
> +++ b/lib/test_hmm.c
> @@ -201,7 +201,13 @@ static void dmirror_do_update(struct dmirror *dmirror, unsigned long start,
> * The XArray doesn't hold references to pages since it relies on
> * the mmu notifier to clear page pointers when they become stale.
> * Therefore, it is OK to just clear the entry.
> + * However, if the entire address space is being invalidated, it
> + * takes too long to clear them one at a time so destroy the array.
> */
> + if (start == 0 && end == ULONG_MAX) {
> + xa_destroy(&dmirror->pt);
> + return;
> + }
> for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++)
> xa_erase(&dmirror->pt, pfn);
> }
Just use xa_for_each_range() instead of the naive loop, it already
optimizes against membership and avoids the need for the xa_destroy
hack
Jason
On 5/15/20 4:15 PM, Jason Gunthorpe wrote:
> On Wed, May 13, 2020 at 02:45:07PM -0700, Ralph Campbell wrote:
>> The test driver uses an xa_array to store virtual to physical address
>> translations for a simulated hardware device. The MMU notifier
>> invalidation callback is used to keep the table consistent with the CPU
>> page table and is frequently called only for a page or two. However, if
>> the test process exits unexpectedly or is killed, the range can be
>> [0..ULONG_MAX] in which case calling xa_erase() for every possible PFN
>> results in CPU timeouts. Munmap() can result in a large range being
>> invalidated but in that case, the xa_array is likely to contain entries
>> that need to be invalidated.
>> Check for [0..ULONG_MAX] explicitly and just destroy the whole table.
>>
>> Signed-off-by: Ralph Campbell <[email protected]>
>>
>> This patch is based on Jason Gunthorpe's hmm tree and should be folded
>> into the ("mm/hmm/test: add selftest driver for HMM") patch once this
>> patch is reviewed, etc.
>>
>> lib/test_hmm.c | 6 ++++++
>> 1 file changed, 6 insertions(+)
>>
>> diff --git a/lib/test_hmm.c b/lib/test_hmm.c
>> index 8b36c26b717b..b89852ec3c29 100644
>> +++ b/lib/test_hmm.c
>> @@ -201,7 +201,13 @@ static void dmirror_do_update(struct dmirror *dmirror, unsigned long start,
>> * The XArray doesn't hold references to pages since it relies on
>> * the mmu notifier to clear page pointers when they become stale.
>> * Therefore, it is OK to just clear the entry.
>> + * However, if the entire address space is being invalidated, it
>> + * takes too long to clear them one at a time so destroy the array.
>> */
>> + if (start == 0 && end == ULONG_MAX) {
>> + xa_destroy(&dmirror->pt);
>> + return;
>> + }
>> for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++)
>> xa_erase(&dmirror->pt, pfn);
>> }
>
> Just use xa_for_each_range() instead of the naive loop, it already
> optimizes against membership and avoids the need for the xa_destroy
> hack
>
> Jason
>
For some reason I had looked at that and rejected it but of course, it works
fine. :-)
Thanks!