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Re: [PATCH v2 07/18] KVM/MIPS32: MMU/TLB operations for the Guest.

To: Sanjay Lal <sanjayl@kymasys.com>
Subject: Re: [PATCH v2 07/18] KVM/MIPS32: MMU/TLB operations for the Guest.
From: Gleb Natapov <gleb@redhat.com>
Date: Sat, 16 Feb 2013 18:21:45 +0200
Cc: kvm@vger.kernel.org, linux-mips@linux-mips.org
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On Sat, Feb 16, 2013 at 10:57:22AM -0500, Sanjay Lal wrote:
> 
> On Feb 15, 2013, at 1:41 PM, Gleb Natapov wrote:
> 
> > On Fri, Feb 15, 2013 at 01:19:29PM -0500, Sanjay Lal wrote:
> >> 
> >> On Feb 6, 2013, at 7:08 AM, Gleb Natapov wrote:
> >> 
> >>>> 
> >>>> +static void kvm_mips_map_page(struct kvm *kvm, gfn_t gfn)
> >>>> +{
> >>>> +        pfn_t pfn;
> >>>> +
> >>>> +        if (kvm->arch.guest_pmap[gfn] != KVM_INVALID_PAGE)
> >>>> +                return;
> >>>> +
> >>>> +        pfn =kvm_mips_gfn_to_pfn(kvm, gfn);
> >>> This call should be in srcu read section since it access memory slots 
> >>> which
> >>> are srcu protected. You should test with RCU debug enabled.
> >> 
> >> kvm_mips_gfn_to_pfn just maps to gfn_to_pfn. I don't see an instance where 
> >> gfn_to_pfn is in a scru read section?
> >> 
> > Where are you looking?  On x86 if vcpu is not in a guest mode it is in
> > srcu read section. The lock is taken immediately after exit and released
> > before entry. This is because x86 access memory slots a lot. Other
> > arches, that do not access memory slots as much, take the lock around
> > each individual access. As far as I see this is the only place in MIPS
> > kvm where this is needed.
> 
> Ah I see what you mean.  I'll wrap the access in a scru read section.
> 
Thanks.

I think there is userspace triggerable panic() in kvm_mips_map_page().
See my original reply. Just making sure you haven't missed it :)

--
                        Gleb.

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