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From: Christian Borntraeger <borntraeger@de.ibm.com>
To: David Hildenbrand <david@redhat.com>,
	Janosch Frank <frankja@linux.vnet.ibm.com>
Cc: KVM <kvm@vger.kernel.org>, Cornelia Huck <cohuck@redhat.com>,
	Thomas Huth <thuth@redhat.com>,
	Ulrich Weigand <Ulrich.Weigand@de.ibm.com>,
	Claudio Imbrenda <imbrenda@linux.ibm.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	linux-s390 <linux-s390@vger.kernel.org>,
	Michael Mueller <mimu@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
	Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH 01/35] mm:gup/writeback: add callbacks for inaccessible pages
Date: Mon, 10 Feb 2020 19:28:34 +0100	[thread overview]
Message-ID: <f7065c72-0487-9d03-a286-f75a60b4ac5f@de.ibm.com> (raw)
In-Reply-To: <d8622308-6089-50a4-54e0-277dc7c8c74b@redhat.com>



On 10.02.20 19:17, David Hildenbrand wrote:
> On 07.02.20 12:39, Christian Borntraeger wrote:
>> From: Claudio Imbrenda <imbrenda@linux.ibm.com>
>>
>> With the introduction of protected KVM guests on s390 there is now a
>> concept of inaccessible pages. These pages need to be made accessible
>> before the host can access them.
>>
>> While cpu accesses will trigger a fault that can be resolved, I/O
>> accesses will just fail.  We need to add a callback into architecture
>> code for places that will do I/O, namely when writeback is started or
>> when a page reference is taken.
> 
> My question would be: What guarantees that the page will stay accessible
> (for I/O)? IIRC, pages can be converted back to secure/inaccessible
> whenever the guest wants to access them. How will that be dealt with?

Yes, in patch 5 we do use the page lock, PageWriteBack and page_ref_freeze
to only make the page secure again if no I/O is going to be started or
still running.

We have minimized the common code impact (just these 3 callbacks) so that 
architecture code can do the right thing.

> 
> I would assume some magic counter that tracks if the page still has to
> remain accessible. Once all clients that require the page to be
> "accessible" on the I/O path are done, the page can be made inaccessible
> again. But then, I would assume there would be something like a
> 
> /* make page accessible and make sure the page will remain accessible */
> arch_get_page_accessible(page);
> 
> /* we're done dealing with the page content */
> arch_put_page_accessible(page);
> 
> You mention page references. I think you should elaborate how that is
> expected to work in the patch description more detailed.
> 
> 
> (side note: I assume you guys have a plan for dealing with kdump wanting
> to dump inaccessible pages. the kexec kernel would have to talk to the
> UV to convert pages - and also make pages accessible on the I/O path I
> guess - or one would want to mark and skip encrypted pages completely in
> kdump somehow, as the content is essentially garbage)

On kexec and kdump the ultravisor is called as part of the the diagnose
308 subcodes 0 and 1 to make sure that a: kdump works (no fault on a 
previously secure page) and b: the content of the secure page is no 
longer accessible.




  reply	other threads:[~2020-02-10 18:28 UTC|newest]

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-07 11:39 [PATCH 00/35] KVM: s390: Add support for protected VMs Christian Borntraeger
2020-02-07 11:39 ` [PATCH 01/35] mm:gup/writeback: add callbacks for inaccessible pages Christian Borntraeger
2020-02-10 17:27   ` Christian Borntraeger
2020-02-11 11:26     ` Will Deacon
2020-02-11 11:43       ` Christian Borntraeger
2020-02-13 14:48       ` Christian Borntraeger
2020-02-18 16:02         ` Will Deacon
2020-02-13 19:56     ` Sean Christopherson
2020-02-13 20:13       ` Christian Borntraeger
2020-02-13 20:46         ` Sean Christopherson
2020-02-17 20:55         ` Tom Lendacky
2020-02-17 21:14           ` Christian Borntraeger
2020-02-10 18:17   ` David Hildenbrand
2020-02-10 18:28     ` Christian Borntraeger [this message]
2020-02-10 18:43       ` David Hildenbrand
2020-02-10 18:51         ` Christian Borntraeger
2020-02-18  3:36   ` Tian, Kevin
2020-02-18  6:44     ` Christian Borntraeger
2020-02-07 11:39 ` [PATCH 02/35] KVM: s390/interrupt: do not pin adapter interrupt pages Christian Borntraeger
2020-02-10 12:26   ` David Hildenbrand
2020-02-10 18:38     ` Christian Borntraeger
2020-02-10 19:33       ` David Hildenbrand
2020-02-11  9:23         ` [PATCH v2 RFC] " Christian Borntraeger
2020-02-12 11:52           ` Christian Borntraeger
2020-02-12 12:16           ` David Hildenbrand
2020-02-12 12:22             ` Christian Borntraeger
2020-02-12 12:47               ` David Hildenbrand
2020-02-12 12:39           ` Cornelia Huck
2020-02-12 12:44             ` Christian Borntraeger
2020-02-12 13:07               ` Cornelia Huck
2020-02-10 18:56     ` [PATCH 02/35] KVM: s390/interrupt: do not pin adapter interrupt Ulrich Weigand
2020-02-10 12:40   ` [PATCH 02/35] KVM: s390/interrupt: do not pin adapter interrupt pages David Hildenbrand
2020-02-07 11:39 ` [PATCH 05/35] s390/mm: provide memory management functions for protected KVM guests Christian Borntraeger
2020-02-12 13:42   ` Cornelia Huck
2020-02-13  7:43     ` Christian Borntraeger
2020-02-13  8:44       ` Cornelia Huck
2020-02-14 17:59   ` David Hildenbrand
2020-02-14 21:17     ` Christian Borntraeger
2020-02-07 11:39 ` [PATCH 06/35] s390/mm: add (non)secure page access exceptions handlers Christian Borntraeger
2020-02-14 18:05   ` David Hildenbrand
2020-02-14 19:59     ` Christian Borntraeger
2020-02-07 11:39 ` [PATCH 10/35] KVM: s390: protvirt: Secure memory is not mergeable Christian Borntraeger
2020-02-07 11:39 ` [PATCH 11/35] KVM: s390/mm: Make pages accessible before destroying the guest Christian Borntraeger
2020-02-14 18:40   ` David Hildenbrand
2020-02-07 11:39 ` [PATCH 21/35] KVM: s390/mm: handle guest unpin events Christian Borntraeger
2020-02-10 14:58   ` Thomas Huth
2020-02-11 13:21     ` Cornelia Huck

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