Re: [PATCH] kvm: rework remove-write-access for a slot

[Avi Kivity]

On 06/04/2010 11:14 AM, Lai Jiangshan wrote:
> > - I thought of a different approach to write protection: write protect
> > the L4 sptes, on write fault add write permission to the L4 spte and
> > write protect the L3 sptes that it points to, etc.  This method can use
> > the slot bitmap to reduce the number of write faults.  However we can
> > reintroduce the slot bitmap if/when we use the method, this shouldn't
> > block the patch.
> >      
> It is very a good approach and it is blazing fast.
>
> I have no time to implement it currently,
> could you update it into the TODO list?
>    

Done.

> > > +static void rmapp_remove_write_access(struct kvm *kvm, unsigned long
> > > *rmapp)
> > > +{
> > > +    u64 *spte = rmap_next(kvm, rmapp, NULL);
> > > +
> > > +    while (spte) {
> > > +        /* avoid RMW */
> > > +        if (is_writable_pte(*spte))
> > > +            *spte&= ~PT_WRITABLE_MASK;
> > >        
> > Must use an atomic operation here to avoid losing dirty or accessed bit.
> >
> >      
> Atomic operation is too expensive, I retained the comment "/* avoid RMW */"
> and wait someone take a good approach for it.
>    

You are right, it is an existing problem.  I just posted a patchset 
which fixes the problem, when it's merged please rebase on top.

--
error compiling committee.c: too many arguments to function

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