Re: [PATCH 01/10] KVM: SVM: Don't use kmap_atomic in nested_svm_map

Avi Kivity
2010-02-18T13:41:12Z

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