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From: Jan Beulich <jbeulich@suse.com>
To: Tamas K Lengyel <tamas.lengyel@intel.com>
Cc: "Tamas K Lengyel" <tamas@tklengyel.com>,
	"Andrew Cooper" <andrew.cooper3@citrix.com>,
	"George Dunlap" <george.dunlap@citrix.com>,
	"Roger Pau Monné" <roger.pau@citrix.com>, "Wei Liu" <wl@xen.org>,
	xen-devel@lists.xenproject.org
Subject: Re: [PATCH v2] x86/mem_sharing: Resolve mm-lock order violations when forking VMs with nested p2m
Date: Thu, 7 Jan 2021 14:55:35 +0100	[thread overview]
Message-ID: <355cf640-6027-816d-70c5-9a4ed445eb9c@suse.com> (raw)
In-Reply-To: <253be1190a5cdc452611b3741d852d1c7d2bc8d4.1610025394.git.tamas.lengyel@intel.com>

On 07.01.2021 14:23, Tamas K Lengyel wrote:
> Several lock-order violations have been encountered while attempting to fork
> VMs with nestedhvm=1 set. This patch resolves the issues.
> 
> The order violations stems from a call to p2m_flush_nestedp2m being performed
> whenever the hostp2m changes. This functions always takes the p2m lock for the
> nested_p2m. However, with sharing the p2m locks always have to be taken before
> the sharing lock. To resolve this issue we avoid taking the sharing lock where
> possible (and was actually unecessary to begin with). But we also make
> p2m_flush_nestedp2m aware that the p2m lock may have already been taken and
> preemptively take all nested_p2m locks before unsharing a page where taking the
> sharing lock is necessary.
> 
> Signed-off-by: Tamas K Lengyel <tamas.lengyel@intel.com>

Acked-by: Jan Beulich <jbeulich@suse.com>


  reply	other threads:[~2021-01-07 13:55 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-07 13:23 [PATCH v2] x86/mem_sharing: Resolve mm-lock order violations when forking VMs with nested p2m Tamas K Lengyel
2021-01-07 13:55 ` Jan Beulich [this message]
2021-01-07 13:57   ` Tamas K Lengyel

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