Messages in this thread | | | Date | Thu, 15 Aug 2019 22:48:35 +0530 | From | Bharath Vedartham <> | Subject | Re: [Question-kvm] Can hva_to_pfn_fast be executed in interrupt context? |
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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 > > >
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