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 12:08:46 -0400
From:	Bandan Das <bsd@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	Jan Kiszka <jan.kiszka@...mens.com>, 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

Paolo Bonzini <pbonzini@...hat.com> writes:

> 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.

So, block on a failure hoping that eventually it will succeed ?

> 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.

Sorry Paolo, I missed your point. Isn't the allocation already GFP_KERNEL ?

> Paolo
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