Messages in this thread | | | Date | Thu, 18 Feb 2010 17:16:37 +0100 | From | Joerg Roedel <> | Subject | Re: [PATCH 01/10] KVM: SVM: Don't use kmap_atomic in nested_svm_map |
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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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