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From: David Woodhouse <dwmw2@infradead.org>
To: Paolo Bonzini <pbonzini@redhat.com>,
	Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: butterflyhuangxx@gmail.com, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org, seanjc@google.com,
	Cornelia Huck <cohuck@redhat.com>,
	Janosch Frank <frankja@linux.ibm.com>,
	David Hildenbrand <david@redhat.com>,
	linux-s390 <linux-s390@vger.kernel.org>,
	Thomas Huth <thuth@redhat.com>,
	Claudio Imbrenda <imbrenda@linux.ibm.com>
Subject: Re: KVM: Warn if mark_page_dirty() is called without an active vCPU
Date: Thu, 13 Jan 2022 12:30:19 +0000	[thread overview]
Message-ID: <b6d9785d769f98da0b057fac643b0f088e346a94.camel@infradead.org> (raw)
In-Reply-To: <e9e5521d-21e5-8f6f-902c-17b0516b9839@redhat.com>

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On Thu, 2022-01-13 at 13:14 +0100, Paolo Bonzini wrote:
> On 1/13/22 13:06, Christian Borntraeger wrote:
> > From: Christian Borntraeger<
> > borntraeger@de.ibm.com
> > >
> > 
> > Quick heads-up.
> > The new warnon triggers on s390. Here we write to the guest from an
> > irqfd worker. Since we do not use dirty_ring yet this might be an
> > over-indication.
> > Still have to look into that.
> 
> Yes, it's okay to add an #ifdef around the warning.

That would be #ifndef CONFIG_HAVE_KVM_DIRTY_RING, yes? 

I already found it hard to write down the rules around how
kvm_vcpu_write_guest() doesn't use the vCPU it's passed, and how both
it and kvm_write_guest() need to be invoked on a pCPU which currently
owns *a* vCPU belonging to the same KVM... if we add "unless you're on
an architecture that doesn't support dirty ring logging", you may have
to pass me a bucket.

Are you proposing that as an officially documented part of the already
horrid API, or a temporary measure :)

Btw, that get_map_page() in arch/s390/kvm/interrupt.c looks like it has
the same use-after-free problem that kvm_map_gfn() used to have. It
probably wants converting to the new gfn_to_pfn_cache. 

Take a look at how I resolve the same issue for delivering Xen event
channel interrupts.

Although I gave myself a free pass on the dirty marking in that case,
by declaring that the shinfo page doesn't get marked dirty; it should
be considered *always* dirty. You might have less fun declaring that
retrospectively in your case.

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  parent reply	other threads:[~2022-01-13 12:30 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-18 17:14 There is a null-ptr-deref bug in kvm_dirty_ring_get in virt/kvm/dirty_ring.c butt3rflyh4ck
2021-10-21 20:08 ` Paolo Bonzini
2021-10-28  7:42   ` butt3rflyh4ck
2021-11-08  5:11   ` butt3rflyh4ck
2021-11-16 15:41   ` butt3rflyh4ck
2021-11-16 16:22   ` [EXTERNAL] " David Woodhouse
2021-11-16 17:07     ` David Woodhouse
2021-11-17  9:46   ` Woodhouse, David
2021-11-17 16:49     ` Paolo Bonzini
2021-11-17 18:10       ` Woodhouse, David
2021-11-20 10:16   ` KVM: Warn if mark_page_dirty() is called without an active vCPU David Woodhouse
2021-11-22 17:01     ` Sean Christopherson
2021-11-22 17:52       ` David Woodhouse
2021-11-22 18:49         ` Sean Christopherson
2022-01-13 12:06     ` Christian Borntraeger
2022-01-13 12:14       ` Paolo Bonzini
2022-01-13 12:29         ` [PATCH] KVM: avoid warning on s390 in mark_page_dirty Christian Borntraeger
2022-01-13 12:31           ` David Woodhouse
2022-01-18  8:37           ` Christian Borntraeger
2022-01-18  8:44             ` Paolo Bonzini
2022-01-18  8:53               ` Christian Borntraeger
2022-01-18 11:44                 ` Paolo Bonzini
2022-01-13 12:30         ` David Woodhouse [this message]
2022-01-13 12:51           ` KVM: Warn if mark_page_dirty() is called without an active vCPU Christian Borntraeger
2022-01-13 13:22             ` David Woodhouse
2022-01-13 15:09               ` Christian Borntraeger
2022-01-13 14:36           ` Paolo Bonzini

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