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From: Avi Kivity on 18 Feb 2010 08:50
On 02/18/2010 01:38 PM, Joerg Roedel wrote:
> Use of kmap_atomic disables preemption but if we run in
> shadow-shadow mode the vmrun emulation executes kvm_set_cr3
> which might sleep or fault. So use kmap instead for
> nested_svm_map.
>
>
>
> -static void nested_svm_unmap(void *addr, enum km_type idx)
> +static void nested_svm_unmap(void *addr)
> {
> struct page *page;
>
> @@ -1443,7 +1443,7 @@ static void nested_svm_unmap(void *addr, enum km_type idx)
>
> page = kmap_atomic_to_page(addr);
>
> - kunmap_atomic(addr, idx);
> + kunmap(addr);
> kvm_release_page_dirty(page);
> }
>

kunmap() takes a struct page *, not the virtual address (a consistent
source of bugs).

kmap() is generally an unloved interface, it is slow and possibly
deadlock prone, but it's better than sleeping in atomic context. If you
can hack your way around it, that is preferred.

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

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From: Joerg Roedel on 18 Feb 2010 11:20
On Thu, Feb 18, 2010 at 03:40:56PM +0200, Avi Kivity wrote:
> On 02/18/2010 01:38 PM, Joerg Roedel wrote:
> >Use of kmap_atomic disables preemption but if we run in
> >shadow-shadow mode the vmrun emulation executes kvm_set_cr3
> >which might sleep or fault. So use kmap instead for
> >nested_svm_map.
> >
> >
> >
> >-static void nested_svm_unmap(void *addr, enum km_type idx)
> >+static void nested_svm_unmap(void *addr)
> > {
> > struct page *page;
> >
> >@@ -1443,7 +1443,7 @@ static void nested_svm_unmap(void *addr, enum km_type idx)
> >
> > page = kmap_atomic_to_page(addr);
> >
> >- kunmap_atomic(addr, idx);
> >+ kunmap(addr);
> > kvm_release_page_dirty(page);
> > }
>
> kunmap() takes a struct page *, not the virtual address (a
> consistent source of bugs).

Ah true, thanks. I'll fix that.

> kmap() is generally an unloved interface, it is slow and possibly
> deadlock prone, but it's better than sleeping in atomic context. If
> you can hack your way around it, that is preferred.

Best would be to use kvm_read_guest, but I fear that this will have an
performance impact. Maybe I'll try this and measure if it really has a
significant performance impact.

Joerg


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