linux-kernel - Re: [PATCH] KVM: nVMX: Don't return error on nested bitmap memory allocation failure

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Date:	Wed, 29 Apr 2015 15:23:58 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Jan Kiszka <jan.kiszka@...mens.com>, Bandan Das <bsd@...hat.com>
CC:	kvm@...r.kernel.org, Wincy Van <fanwenyi0529@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: nVMX: Don't return error on nested bitmap memory
 allocation failure



On 29/04/2015 15:05, Jan Kiszka wrote:
> > Yeah... I hear you. Ok, let me put it this way - Assume that we can
> > defer this allocation up until the point that the nested subsystem is
> > actually used i.e L1 tries running a guest and we try to allocate this
> > area. If get_free_page() failed in that case, would we still want to
> > kill L1 too ? I guess no.
>
> We could block the hypervisor thread on the allocation, just like it
> would block on faults for swapped out pages or new ones that have to be
> reclaimed from the page cache first.

In that case we should avoid making the allocation GFP_ATOMIC to begin with.

If a GFP_KERNEL allocation failed, returning -ENOMEM from KVM_RUN (which
practically means killing the guest) would actually be a very real
possibility.

Paolo
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