From: David Hildenbrand <david@redhat.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>,
Thomas Huth <thuth@redhat.com>,
kvm@vger.kernel.org, Janosch Frank <frankja@linux.ibm.com>
Cc: linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-s390@vger.kernel.org, "Cornelia Huck" <cohuck@redhat.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>,
"Shuah Khan" <shuah@kernel.org>, "Peter Xu" <peterx@redhat.com>
Subject: Re: [PATCH 2/2] KVM: selftests: Enable dirty_log_test on s390x
Date: Wed, 31 Jul 2019 13:06:03 +0200 [thread overview]
Message-ID: <03e7f73e-2b21-688b-83c6-c10eaafdebd5@redhat.com> (raw)
In-Reply-To: <341c3705-c2cb-9e87-cc03-42e0cefba308@de.ibm.com>
On 30.07.19 20:04, Christian Borntraeger wrote:
>
>
> On 30.07.19 19:11, Thomas Huth wrote:
>> On 30/07/2019 16.57, Christian Borntraeger wrote:
>>>
>>>
>>> On 30.07.19 12:01, Thomas Huth wrote:
>>>> To run the dirty_log_test on s390x, we have to make sure that we
>>>> access the dirty log bitmap with little endian byte ordering and
>>>> we have to properly align the memslot of the guest.
>>>> Also all dirty bits of a segment are set once on s390x when one
>>>> of the pages of a segment are written to for the first time, so
>>>> we have to make sure that we touch all pages during the first
>>>> iteration to keep the test in sync here.
>>>
>>> While this fixes the test (and the migration does work fine), it still
>>> means that s390x overindicates the dirty bit for sparsely populated
>>> 1M segments. It is just a performance issue, but maybe we should try
>>> to get this fixed.
>>
>> I hope you don't expect me to fix this - the gmap code is really not my
>> turf...
>
> No, this is clearly on our turf.
FWIW, we share the pagetables with the userspace process. We mark a page
as dirty (PGSTE_UC_BIT) when
- We modify the storage key
- We map a PTE as RW (pgste_set_pte())
I assume all PTEs of the segment are mapped RW (for example, if user
space wrote to such a PTE), that is why we have the PGSTE_UC_BIT bit set.
As PGSTE_UC_BIT also tracks what userspace did, not only KVM via the
GMAP, this might indeed be correct.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2019-07-31 11:06 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-30 10:01 [PATCH 0/2] KVM: selftests: Enable ucall and dirty_log_test on s390x Thomas Huth
2019-07-30 10:01 ` [PATCH 1/2] KVM: selftests: Implement ucall() for s390x Thomas Huth
2019-07-30 10:48 ` Andrew Jones
2019-07-31 9:43 ` Thomas Huth
2019-07-31 10:28 ` Andrew Jones
2019-07-31 11:16 ` Thomas Huth
2019-07-31 12:57 ` Paolo Bonzini
2019-07-31 13:05 ` Andrew Jones
2019-07-30 10:01 ` [PATCH 2/2] KVM: selftests: Enable dirty_log_test on s390x Thomas Huth
2019-07-30 10:57 ` Andrew Jones
2019-07-31 8:19 ` Thomas Huth
2019-07-31 8:44 ` Andrew Jones
2019-07-31 12:58 ` Paolo Bonzini
2019-07-30 11:35 ` Paolo Bonzini
2019-07-30 14:57 ` Christian Borntraeger
2019-07-30 17:11 ` Thomas Huth
2019-07-30 18:04 ` Christian Borntraeger
2019-07-31 11:06 ` David Hildenbrand [this message]
2019-07-30 19:06 ` Paolo Bonzini
2019-07-31 7:16 ` Christian Borntraeger
2019-07-30 11:36 ` [PATCH 0/2] KVM: selftests: Enable ucall and " Paolo Bonzini
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