Hi Peter,
On 05/18/2018 07:53 AM, Peter Xu wrote:
> On Thu, May 17, 2018 at 03:39:50PM +0200, Auger Eric wrote:
>> Hi Peter,
>>
>> On 05/04/2018 05:08 AM, Peter Xu wrote:
>>> For UNMAP-only IOMMU notifiers, we don't really need to walk the page
>> s/really// ;-)
>
> Ok.
>
>>> tables. Fasten that procedure by skipping the page table walk. That
>>> should boost performance for UNMAP-only notifiers like vhost.
>>>
>>> Signed-off-by: Peter Xu <pet...@redhat.com>
>>> ---
>>> include/hw/i386/intel_iommu.h | 2 ++
>>> hw/i386/intel_iommu.c | 43 +++++++++++++++++++++++++++++++----
>>> 2 files changed, 40 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/include/hw/i386/intel_iommu.h b/include/hw/i386/intel_iommu.h
>>> index ee517704e7..9e0a6c1c6a 100644
>>> --- a/include/hw/i386/intel_iommu.h
>>> +++ b/include/hw/i386/intel_iommu.h
>>> @@ -93,6 +93,8 @@ struct VTDAddressSpace {
>>> IntelIOMMUState *iommu_state;
>>> VTDContextCacheEntry context_cache_entry;
>>> QLIST_ENTRY(VTDAddressSpace) next;
>>> + /* Superset of notifier flags that this address space has */
>>> + IOMMUNotifierFlag notifier_flags;
>>> };
>>>
>>> struct VTDBus {
>>> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
>>> index 112971638d..9a418abfb6 100644
>>> --- a/hw/i386/intel_iommu.c
>>> +++ b/hw/i386/intel_iommu.c
>>> @@ -138,6 +138,12 @@ static inline void vtd_iommu_unlock(IntelIOMMUState *s)
>>> qemu_mutex_unlock(&s->iommu_lock);
>>> }
>>>
>>> +/* Whether the address space needs to notify new mappings */
>>> +static inline gboolean vtd_as_notify_mappings(VTDAddressSpace *as)
>> would suggest vtd_as_has_map_notifier()? But tastes & colours ;-)
>
> Yeah it is. But okay, I can switch to that especially it's only used
> in this patch and it's new.
>
>>> +{
>>> + return as->notifier_flags & IOMMU_NOTIFIER_MAP;
>>> +}
>>> +
>>> /* GHashTable functions */
>>> static gboolean vtd_uint64_equal(gconstpointer v1, gconstpointer v2)
>>> {
>>> @@ -1433,14 +1439,35 @@ static void
>>> vtd_iotlb_page_invalidate_notify(IntelIOMMUState *s,
>>> VTDAddressSpace *vtd_as;
>>> VTDContextEntry ce;
>>> int ret;
>>> + hwaddr size = (1 << am) * VTD_PAGE_SIZE;
>>>
>>> QLIST_FOREACH(vtd_as, &(s->notifiers_list), next) {
>>> ret = vtd_dev_to_context_entry(s, pci_bus_num(vtd_as->bus),
>>> vtd_as->devfn, &ce);
>>> if (!ret && domain_id == VTD_CONTEXT_ENTRY_DID(ce.hi)) {
>>> - vtd_page_walk(&ce, addr, addr + (1 << am) * VTD_PAGE_SIZE,
>>> - vtd_page_invalidate_notify_hook,
>>> - (void *)&vtd_as->iommu, true, s->aw_bits);
>>> + if (vtd_as_notify_mappings(vtd_as)) {
>>> + /*
>>> + * For MAP-inclusive notifiers, we need to walk the
>>> + * page table to sync the shadow page table.
>>> + */
>> Potentially we may have several notifiers attached to the IOMMU MR ~
>> vtd_as, each of them having different flags. Those flags are OR'ed in
>> memory_region_update_iommu_notify_flags and this is the one you now
>> store in the vtd_as. So maybe your comment may rather state:
>> as soon as we have at least one MAP notifier, we need to do the PTW?
>
> Actually this is not 100% clear too, since all the "MAP notifiers" are
> actually both MAP+UNMAP notifiers... Maybe:
Can't IOMMU_NOTIFIER_MAP flag value be used without
IOMMU_NOTIFIER_UNMAP? I don't see such restriction in the
memory_region_register_iommu_notifier API.
>
> As long as we have MAP notifications registered in any of our IOMMU
> notifiers, we need to sync the shadow page table.
>
>>
>> nit: not related to this patch: vtd_page_walk kerneldoc comments misses
>> @notify_unmap param comment
>> side note: the name of the hook is a bit misleading as it suggests we
>> invalidate the entry, whereas we update any valid entry and invalidate
>> stale ones (if notify_unmap=true)?
>>> + vtd_page_walk(&ce, addr, addr + size,
>>> + vtd_page_invalidate_notify_hook,
>>> + (void *)&vtd_as->iommu, true, s->aw_bits);
>>> + } else {
>>> + /*
>>> + * For UNMAP-only notifiers, we don't need to walk the
>>> + * page tables. We just deliver the PSI down to
>>> + * invalidate caches.
>>
>> We just unmap the range?
>
> Isn't it the same thing? :)
>
> If to be explicit, here we know we only registered UNMAP
> notifications, it's not really "unmap", it's really cache
> invalidations only.
yes you're right I meant We just invalidate the range in cache. The
sentence "We just deliver the PSI down to invalidate caches." was not
crystal clear to me at first reading.
Thanks
Eric
>
>>> + */
>>> + IOMMUTLBEntry entry = {
>>> + .target_as = &address_space_memory,
>>> + .iova = addr,
>>> + .translated_addr = 0,
>>> + .addr_mask = size - 1,
>>> + .perm = IOMMU_NONE,
>>> + };
>>> + memory_region_notify_iommu(&vtd_as->iommu, entry);
>>> + }
>>> }
>>> }
>>> }
>>> @@ -2380,6 +2407,9 @@ static void
>>> vtd_iommu_notify_flag_changed(IOMMUMemoryRegion *iommu,
>>> exit(1);
>>> }
>>>
>>> + /* Update per-address-space notifier flags */
>>> + vtd_as->notifier_flags = new;
>>> +
>>> if (old == IOMMU_NOTIFIER_NONE) {
>>> /* Insert new ones */
>>> QLIST_INSERT_HEAD(&s->notifiers_list, vtd_as, next);
>>> @@ -2890,8 +2920,11 @@ static void vtd_iommu_replay(IOMMUMemoryRegion
>>> *iommu_mr, IOMMUNotifier *n)
>>> PCI_FUNC(vtd_as->devfn),
>>> VTD_CONTEXT_ENTRY_DID(ce.hi),
>>> ce.hi, ce.lo);
>>> - vtd_page_walk(&ce, 0, ~0ULL, vtd_replay_hook, (void *)n, false,
>>> - s->aw_bits);
>>> + if (vtd_as_notify_mappings(vtd_as)) {
>>> + /* This is required only for MAP typed notifiers */
>>> + vtd_page_walk(&ce, 0, ~0ULL, vtd_replay_hook, (void *)n, false,
>>> + s->aw_bits);
>>> + }
>>> } else {
>>> trace_vtd_replay_ce_invalid(bus_n, PCI_SLOT(vtd_as->devfn),
>>> PCI_FUNC(vtd_as->devfn));
>>>
>> A worthwhile improvement indeed!
>
> I hope so. :) Thanks,
>
