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From: David Hildenbrand <david@redhat.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>,
	Janosch Frank <frankja@linux.vnet.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>
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>,
	linux-s390 <linux-s390@vger.kernel.org>,
	Michael Mueller <mimu@linux.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	linux-mm@kvack.org, Will Deacon <will@kernel.org>,
	Sean Christopherson <sean.j.christopherson@intel.com>
Subject: Re: [PATCH v2 01/42] mm:gup/writeback: add callbacks for inaccessible pages
Date: Mon, 17 Feb 2020 10:14:55 +0100
Message-ID: <107a8a72-b745-26f2-5805-c4d99ce77b35@redhat.com> (raw)
In-Reply-To: <20200214222658.12946-2-borntraeger@de.ibm.com>

On 14.02.20 23:26, 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.
> 
> This is not only to enable paging, file backing etc, it is also
> necessary to protect the host against a malicious user space. For
> example a bad QEMU could simply start direct I/O on such protected
> memory.  We do not want userspace to be able to trigger I/O errors and
> thus we the logic is "whenever somebody accesses that page (gup) or
> doing I/O, make sure that this page can be accessed. When the guest
> tries to access that page we will wait in the page fault handler for
> writeback to have finished and for the page_ref to be the expected
> value.
> 
> If wanted by others, the callbacks can be extended with error handlin
> and a parameter from where this is called.

s/handlin/handling/

One last question from my side:

Why is it OK to ignore errors here. IOW, why not squash "[PATCH v2
39/42] example for future extension: mm:gup/writeback: add callbacks for
inaccessible pages: error cases" into this patch.

I can see in patch "[PATCH v2 05/42] s390/mm: provide memory management
functions for protected KVM guests", that the call can fail for various
reasons. That puzzles me a bit - what would happen if any of that fails?
Or will it actually never fail for s390x (and all that error handling in
arch_make_page_accessible() is essentially dead code in real life?)

-- 
Thanks,

David / dhildenb


  reply index

Thread overview: 132+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-14 22:26 [PATCH v2 00/42] KVM: s390: Add support for protected VMs Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 01/42] mm:gup/writeback: add callbacks for inaccessible pages Christian Borntraeger
2020-02-17  9:14   ` David Hildenbrand [this message]
2020-02-17 11:10     ` Christian Borntraeger
2020-02-18  8:27       ` David Hildenbrand
2020-02-18 15:46         ` Sean Christopherson
2020-02-18 16:02           ` Will Deacon
2020-02-18 16:15             ` Christian Borntraeger
2020-02-18 21:35               ` Sean Christopherson
2020-02-19  8:31                 ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 02/42] KVM: s390/interrupt: do not pin adapter interrupt pages Christian Borntraeger
2020-02-17  9:43   ` David Hildenbrand
2020-02-20 12:18     ` David Hildenbrand
2020-02-20 13:31     ` Christian Borntraeger
2020-02-20 13:34       ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 03/42] s390/protvirt: introduce host side setup Christian Borntraeger
2020-02-17  9:53   ` David Hildenbrand
2020-02-17 11:11     ` Christian Borntraeger
2020-02-17 11:13       ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 04/42] s390/protvirt: add ultravisor initialization Christian Borntraeger
2020-02-17  9:57   ` David Hildenbrand
2020-02-17 11:13     ` Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 05/42] s390/mm: provide memory management functions for protected KVM guests Christian Borntraeger
2020-02-17 10:21   ` David Hildenbrand
2020-02-17 11:28     ` Christian Borntraeger
2020-02-17 12:07       ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 06/42] s390/mm: add (non)secure page access exceptions handlers Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 07/42] KVM: s390: protvirt: Add UV debug trace Christian Borntraeger
2020-02-17 10:41   ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 08/42] KVM: s390: add new variants of UV CALL Christian Borntraeger
2020-02-17 10:42   ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 09/42] KVM: s390: protvirt: Add initial vm and cpu lifecycle handling Christian Borntraeger
2020-02-17 10:56   ` David Hildenbrand
2020-02-17 12:04     ` Christian Borntraeger
2020-02-17 12:09       ` David Hildenbrand
2020-02-17 14:53         ` [PATCH 0/2] example changes Christian Borntraeger
2020-02-17 14:53           ` [PATCH 1/2] lock changes Christian Borntraeger
2020-02-17 14:53           ` [PATCH 2/2] merge vm/cpu create Christian Borntraeger
2020-02-17 15:00             ` Janosch Frank
2020-02-17 15:02               ` Christian Borntraeger
2020-02-19 11:02               ` Christian Borntraeger
2020-02-17 19:18           ` [PATCH 0/2] example changes David Hildenbrand
2020-02-18  8:09     ` [PATCH v2 09/42] KVM: s390: protvirt: Add initial vm and cpu lifecycle handling Christian Borntraeger
2020-02-18  8:39   ` [PATCH v2.1] " Christian Borntraeger
2020-02-18  9:12     ` David Hildenbrand
2020-02-18 21:18       ` Christian Borntraeger
2020-02-19  8:32         ` David Hildenbrand
2020-02-19 11:01       ` Christian Borntraeger
2020-02-18  9:56     ` David Hildenbrand
2020-02-18 20:26       ` Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 10/42] KVM: s390: protvirt: Add KVM api documentation Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 11/42] KVM: s390: protvirt: Secure memory is not mergeable Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 12/42] KVM: s390/mm: Make pages accessible before destroying the guest Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 13/42] KVM: s390: protvirt: Handle SE notification interceptions Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 14/42] KVM: s390: protvirt: Instruction emulation Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 15/42] KVM: s390: protvirt: Add interruption injection controls Christian Borntraeger
2020-02-17 10:59   ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 16/42] KVM: s390: protvirt: Implement interruption injection Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 17/42] KVM: s390: protvirt: Add SCLP interrupt handling Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 18/42] KVM: s390: protvirt: Handle spec exception loops Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 19/42] KVM: s390: protvirt: Add new gprs location handling Christian Borntraeger
2020-02-17 11:01   ` David Hildenbrand
2020-02-17 11:33     ` Christian Borntraeger
2020-02-17 14:37     ` Janosch Frank
2020-02-14 22:26 ` [PATCH v2 20/42] KVM: S390: protvirt: Introduce instruction data area bounce buffer Christian Borntraeger
2020-02-17 11:08   ` David Hildenbrand
2020-02-17 14:47     ` Janosch Frank
2020-02-17 15:00       ` Christian Borntraeger
2020-02-17 15:38         ` Janosch Frank
2020-02-17 16:58           ` Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 21/42] KVM: s390: protvirt: handle secure guest prefix pages Christian Borntraeger
2020-02-17 11:11   ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 22/42] KVM: s390/mm: handle guest unpin events Christian Borntraeger
2020-02-17 14:23   ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 23/42] KVM: s390: protvirt: Write sthyi data to instruction data area Christian Borntraeger
2020-02-17 14:24   ` David Hildenbrand
2020-02-17 18:40     ` Christian Borntraeger
2020-02-17 19:16       ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 24/42] KVM: s390: protvirt: STSI handling Christian Borntraeger
2020-02-18  8:35   ` David Hildenbrand
2020-02-18  8:44     ` Christian Borntraeger
2020-02-18  9:08       ` David Hildenbrand
2020-02-18  9:11         ` Christian Borntraeger
2020-02-18  9:13           ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 25/42] KVM: s390: protvirt: disallow one_reg Christian Borntraeger
2020-02-18  8:40   ` David Hildenbrand
2020-02-18  8:57     ` Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 26/42] KVM: s390: protvirt: Do only reset registers that are accessible Christian Borntraeger
2020-02-18  8:42   ` David Hildenbrand
2020-02-18  9:20     ` Christian Borntraeger
2020-02-18  9:28       ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 27/42] KVM: s390: protvirt: Only sync fmt4 registers Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 28/42] KVM: s390: protvirt: Add program exception injection Christian Borntraeger
2020-02-18  9:33   ` David Hildenbrand
2020-02-18  9:37     ` Christian Borntraeger
2020-02-18  9:39       ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 29/42] KVM: s390: protvirt: Add diag 308 subcode 8 - 10 handling Christian Borntraeger
2020-02-18  9:38   ` David Hildenbrand
2020-02-19 12:45     ` Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 30/42] KVM: s390: protvirt: UV calls in support of diag308 0, 1 Christian Borntraeger
2020-02-18  9:44   ` David Hildenbrand
2020-02-19 11:53     ` Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 31/42] KVM: s390: protvirt: Report CPU state to Ultravisor Christian Borntraeger
2020-02-18  9:48   ` David Hildenbrand
2020-02-19 19:36     ` Christian Borntraeger
2020-02-19 19:46       ` Christian Borntraeger
2020-02-20 10:52         ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 32/42] KVM: s390: protvirt: Support cmd 5 operation state Christian Borntraeger
2020-02-18  9:50   ` David Hildenbrand
2020-02-19 11:06     ` Christian Borntraeger
2020-02-19 11:08       ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 33/42] KVM: s390: protvirt: Mask PSW interrupt bits for interception 104 and 112 Christian Borntraeger
2020-02-18  9:53   ` David Hildenbrand
2020-02-18 10:02     ` David Hildenbrand
2020-02-18 10:05     ` Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 34/42] KVM: s390: protvirt: do not inject interrupts after start Christian Borntraeger
2020-02-18  9:53   ` David Hildenbrand
2020-02-18 10:02     ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 35/42] KVM: s390: protvirt: Add UV cpu reset calls Christian Borntraeger
2020-02-18  9:54   ` David Hildenbrand
2020-02-14 22:26 ` [PATCH v2 36/42] DOCUMENTATION: Protected virtual machine introduction and IPL Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 37/42] s390/uv: Fix handling of length extensions (already in s390 tree) Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 38/42] s390: protvirt: Add sysfs firmware interface for Ultravisor information Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 39/42] example for future extension: mm:gup/writeback: add callbacks for inaccessible pages: error cases Christian Borntraeger
2020-02-18 16:25   ` Will Deacon
2020-02-18 16:30     ` Christian Borntraeger
2020-02-18 16:33       ` Will Deacon
2020-02-14 22:26 ` [PATCH v2 40/42] example for future extension: mm:gup/writeback: add callbacks for inaccessible pages: source indication Christian Borntraeger
2020-02-17 14:15   ` Ulrich Weigand
2020-02-17 14:38     ` Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 41/42] potential fixup for "s390/mm: provide memory management functions for protected KVM guests" Christian Borntraeger
2020-02-14 22:26 ` [PATCH v2 42/42] KVM: s390: rstify new ioctls in api.rst Christian Borntraeger

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