If a page is marked as dirty in the guest pte, set_pte_common() can set the
writable bit on newly-instantiated shadow pte. This optimization avoids
a write fault after the initial read fault.
However, if a write fault instantiates the pte, fix_write_pf() incorrectly
reports the fault as a guest page fault, and the guest oopses on what appears
to be a correctly-mapped page.
Fix is to detect the condition and only report a guest page fault on a user
access to a kernel page.
With the fix, a kvm guest can survive a whole night of running the kernel
hacker's screensaver (make -j9 in a loop).
Signed-off-by: Avi Kivity <[email protected]>
Index: linux-2.6/drivers/kvm/paging_tmpl.h
===================================================================
--- linux-2.6.orig/drivers/kvm/paging_tmpl.h
+++ linux-2.6/drivers/kvm/paging_tmpl.h
@@ -274,7 +274,7 @@ static int FNAME(fix_write_pf)(struct kv
struct kvm_mmu_page *page;
if (is_writeble_pte(*shadow_ent))
- return 0;
+ return !user || (*shadow_ent & PT_USER_MASK);
writable_shadow = *shadow_ent & PT_SHADOW_WRITABLE_MASK;
if (user) {
-
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