From: Anthony Krowiak <akrowiak@linux.ibm.com>
To: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org,
kvm@vger.kernel.org
Cc: jjherne@linux.ibm.com, borntraeger@de.ibm.com, cohuck@redhat.com,
mjrosato@linux.ibm.com, pasic@linux.ibm.com, pbonzini@redhat.com,
frankja@linux.ibm.com, imbrenda@linux.ibm.com, david@redhat.com
Subject: Re: [RFC] kvm: reverse call order of kvm_arch_destroy_vm() and kvm_destroy_devices()
Date: Wed, 27 Jul 2022 15:00:02 -0400 [thread overview]
Message-ID: <647bfead-5d7c-1cb1-3bf2-235ae0205310@linux.ibm.com> (raw)
In-Reply-To: <20220705185430.499688-1-akrowiak@linux.ibm.com>
Any Takers??????
On 7/5/22 2:54 PM, Tony Krowiak wrote:
> There is a new requirement for s390 secure execution guests that the
> hypervisor ensures all AP queues are reset and disassociated from the
> KVM guest before the secure configuration is torn down. It is the
> responsibility of the vfio_ap device driver to handle this.
>
> Prior to commit ("vfio: remove VFIO_GROUP_NOTIFY_SET_KVM"),
> the driver reset all AP queues passed through to a KVM guest when notified
> that the KVM pointer was being set to NULL. Subsequently, the AP queues
> are only reset when the fd for the mediated device used to pass the queues
> through to the guest is closed (the vfio_ap_mdev_close_device() callback).
> This is not a problem when userspace is well-behaved and uses the
> KVM_DEV_VFIO_GROUP_DEL attribute to remove the VFIO group; however, if
> userspace for some reason does not close the mdev fd, a secure execution
> guest will tear down its configuration before the AP queues are
> reset because the teardown is done in the kvm_arch_destroy_vm function
> which is invoked prior to vm_destroy_devices.
>
> This patch proposes a simple solution; rather than introducing a new
> notifier into vfio or callback into KVM, what aoubt reversing the order
> in which the kvm_arch_destroy_vm and kvm_destroy_devices are called. In
> some very limited testing (i.e., the automated regression tests for
> the vfio_ap device driver) this did not seem to cause any problems.
>
> The question remains, is there a good technical reason why the VM
> is destroyed before the devices it is using? This is not intuitive, so
> this is a request for comments on this proposed patch. The assumption
> here is that the medev fd will get closed when the devices are destroyed.
>
> Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
> ---
> virt/kvm/kvm_main.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index a49df8988cd6..edaf2918be9b 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1248,8 +1248,8 @@ static void kvm_destroy_vm(struct kvm *kvm)
> #else
> kvm_flush_shadow_all(kvm);
> #endif
> - kvm_arch_destroy_vm(kvm);
> kvm_destroy_devices(kvm);
> + kvm_arch_destroy_vm(kvm);
> for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
> kvm_free_memslots(kvm, &kvm->__memslots[i][0]);
> kvm_free_memslots(kvm, &kvm->__memslots[i][1]);
next prev parent reply other threads:[~2022-07-27 19:15 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-05 18:54 [RFC] kvm: reverse call order of kvm_arch_destroy_vm() and kvm_destroy_devices() Tony Krowiak
2022-07-05 19:30 ` Matthew Rosato
2022-07-18 14:11 ` Anthony Krowiak
2022-07-27 19:00 ` Anthony Krowiak [this message]
2022-08-01 11:53 ` Halil Pasic
2022-08-11 14:39 ` Anthony Krowiak
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=647bfead-5d7c-1cb1-3bf2-235ae0205310@linux.ibm.com \
--to=akrowiak@linux.ibm.com \
--cc=borntraeger@de.ibm.com \
--cc=cohuck@redhat.com \
--cc=david@redhat.com \
--cc=frankja@linux.ibm.com \
--cc=imbrenda@linux.ibm.com \
--cc=jjherne@linux.ibm.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-s390@vger.kernel.org \
--cc=mjrosato@linux.ibm.com \
--cc=pasic@linux.ibm.com \
--cc=pbonzini@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).