Right now we temporarily take the page table lock in gmap_pmd_op_walk()
even though we know we won't need it (if we can never have 1mb pages
mapped into the gmap).
So let's special case this, so
gmap_protect_range()/gmap_sync_dirty_log_pmd() will not take the lock in
case huge pages are not allowed.
gmap_protect_range() is called quite frequently for managing shadow
page tables in vSIE environments.
Signed-off-by: David Hildenbrand <[email protected]>
---
arch/s390/mm/gmap.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index bb44990c8212..d4fa0a4514e0 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -905,10 +905,16 @@ static inline pmd_t *gmap_pmd_op_walk(struct gmap *gmap, unsigned long gaddr)
pmd_t *pmdp;
BUG_ON(gmap_is_shadow(gmap));
- spin_lock(&gmap->guest_table_lock);
pmdp = (pmd_t *) gmap_table_walk(gmap, gaddr, 1);
+ if (!pmdp)
+ return NULL;
- if (!pmdp || pmd_none(*pmdp)) {
+ /* without huge pages, there is no need to take the table lock */
+ if (!gmap->mm->context.allow_gmap_hpage_1m)
+ return pmd_none(*pmdp) ? NULL : pmdp;
+
+ spin_lock(&gmap->guest_table_lock);
+ if (pmd_none(*pmdp)) {
spin_unlock(&gmap->guest_table_lock);
return NULL;
}
--
2.17.1
On 06.08.2018 17:54, David Hildenbrand wrote:
> Right now we temporarily take the page table lock in gmap_pmd_op_walk()
> even though we know we won't need it (if we can never have 1mb pages
> mapped into the gmap).
>
> So let's special case this, so
> gmap_protect_range()/gmap_sync_dirty_log_pmd() will not take the lock in
> case huge pages are not allowed.
So, let's make this a special case
>
> gmap_protect_range() is called quite frequently for managing shadow
> page tables in vSIE environments.
>
> Signed-off-by: David Hildenbrand <[email protected]>
If you make the patch title more specific:
Reviewed-by: Janosch Frank <[email protected]>
I considered getting rid of the last unlock with the !large check, but
in theory somebody could run a VM with the HPAGE CAP and 4k pages which
would then result in havoc if we wouldn't also adapt gmap_pmd_op_end.
> ---
> arch/s390/mm/gmap.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index bb44990c8212..d4fa0a4514e0 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -905,10 +905,16 @@ static inline pmd_t *gmap_pmd_op_walk(struct gmap *gmap, unsigned long gaddr)
> pmd_t *pmdp;
>
> BUG_ON(gmap_is_shadow(gmap));
> - spin_lock(&gmap->guest_table_lock);
> pmdp = (pmd_t *) gmap_table_walk(gmap, gaddr, 1);
> + if (!pmdp)
> + return NULL;
>
> - if (!pmdp || pmd_none(*pmdp)) {
> + /* without huge pages, there is no need to take the table lock */
> + if (!gmap->mm->context.allow_gmap_hpage_1m)
> + return pmd_none(*pmdp) ? NULL : pmdp;
> +
> + spin_lock(&gmap->guest_table_lock);
> + if (pmd_none(*pmdp)) {
> spin_unlock(&gmap->guest_table_lock);
> return NULL;
> }
>
On 07.08.2018 09:26, Janosch Frank wrote:
> On 06.08.2018 17:54, David Hildenbrand wrote:
>> Right now we temporarily take the page table lock in gmap_pmd_op_walk()
>> even though we know we won't need it (if we can never have 1mb pages
>> mapped into the gmap).
>>
>> So let's special case this, so
>> gmap_protect_range()/gmap_sync_dirty_log_pmd() will not take the lock in
>> case huge pages are not allowed.
>
> So, let's make this a special case
>
>>
>> gmap_protect_range() is called quite frequently for managing shadow
>> page tables in vSIE environments.
>>
>> Signed-off-by: David Hildenbrand <[email protected]>
>
> If you make the patch title more specific:
> Reviewed-by: Janosch Frank <[email protected]>
"s390/mm: optimize locking without huge pages in gmap_pmd_op_walk()"
Thanks!
--
Thanks,
David / dhildenb