From: Bharath Vedartham <linux.bhar@gmail.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: rkrcmar@redhat.com, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
khalid.aziz@oracle.com
Subject: Re: [Question-kvm] Can hva_to_pfn_fast be executed in interrupt context?
Date: Thu, 15 Aug 2019 22:48:35 +0530 [thread overview]
Message-ID: <20190815171834.GA14342@bharath12345-Inspiron-5559> (raw)
In-Reply-To: <54182261-88a4-9970-1c3c-8402e130dcda@redhat.com>
On Tue, Aug 13, 2019 at 10:17:09PM +0200, Paolo Bonzini wrote:
> On 13/08/19 21:14, Bharath Vedartham wrote:
> > Hi all,
> >
> > I was looking at the function hva_to_pfn_fast(in virt/kvm/kvm_main) which is
> > executed in an atomic context(even in non-atomic context, since
> > hva_to_pfn_fast is much faster than hva_to_pfn_slow).
> >
> > My question is can this be executed in an interrupt context?
>
> No, it cannot for the reason you mention below.
>
> Paolo
hmm.. Well I expected the answer to be kvm specific.
Because I observed a similar use-case for a driver (sgi-gru) where
we want to retrive the physical address of a virtual address. This was
done in atomic and non-atomic context similar to hva_to_pfn_fast and
hva_to_pfn_slow. __get_user_pages_fast(for atomic case)
would not work as the driver could execute in interrupt context.
The driver manually walked the page tables to handle this issue.
Since kvm is a widely used piece of code, I asked this question to know
how kvm handled this issue.
Thank you for your time.
Thank you
Bharath
> > The motivation for this question is that in an interrupt context, we cannot
> > assume "current" to be the task_struct of the process of interest.
> > __get_user_pages_fast assume current->mm when walking the process page
> > tables.
> >
> > So if this function hva_to_pfn_fast can be executed in an
> > interrupt context, it would not be safe to retrive the pfn with
> > __get_user_pages_fast.
> >
> > Thoughts on this?
> >
> > Thank you
> > Bharath
> >
>
next prev parent reply other threads:[~2019-08-15 17:18 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-13 19:14 [Question-kvm] Can hva_to_pfn_fast be executed in interrupt context? Bharath Vedartham
2019-08-13 20:17 ` Paolo Bonzini
2019-08-15 17:18 ` Bharath Vedartham [this message]
[not found] ` <CABgObfbQOS28cG_9Ca_2OXbLmDy_hwUkuqPnzJG5=FZ5sEYGfA@mail.gmail.com>
2019-08-20 16:08 ` Bharath Vedartham
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