From mboxrd@z Thu Jan  1 00:00:00 1970
From: Martin Schwidefsky <schwidefsky@de.ibm.com>
Subject: Re: [patch 10/12] [PATCH] kvm-s390: storage key interface
Date: Thu, 15 Dec 2011 18:14:28 +0100
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Cc: Avi Kivity <avi@redhat.com>, Marcelo Tossati <mtosatti@redhat.com>,
	borntrae@linux.vnet.ibm.com, heicars2@linux.vnet.ibm.com,
	mschwid2@linux.vnet.ibm.com, huckc@linux.vnet.ibm.com,
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	Joachim von Buttlar <joachim_von_buttlar@de.ibm.com>,
	Jens Freimann <jfrei@de.ibm.com>, agraf@suse.de
To: Carsten Otte <cotte@de.ibm.com>
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On Thu, 15 Dec 2011 11:28:03 +0100
Carsten Otte <cotte@de.ibm.com> wrote:

> +	case KVM_S390_KEYOP_SSKE:
> +		if (!(vma->vm_flags & (VM_WRITE | VM_MAYWRITE))) {
> +			r = -EACCES;
> +			break;
> +		}

Unfortunately I just realized while discussing with Heiko that a check
for VM_WRITE is not enough. We could still have a read-only pte that
points to a file backed page which is purely read-only. A write access
is allowed but would cause copy-on-write. But we set the storage key
of the original page which would make the read-only page dirty.
We need to solved the race on the dirty bit in a clean way, otherwise
there always will be a corner case.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.