On 06/22/2011 05:36 PM, Xiao Guangrong wrote:
The idea is from Avi:
| We could cache the result of a miss in an spte by using a reserved bit, and
| checking the page fault error code (or seeing if we get an ept violation or
| ept misconfiguration), so if we get repeated mmio on a page, we don't need to
| search the slot list/tree.
| (https://lkml.org/lkml/2011/2/22/221)
When the page fault is caused by mmio, we cache the info in the shadow page
table, and also set the reserved bits in the shadow page table, so if the mmio
is caused again, we can quickly identify it and emulate it directly
Searching mmio gfn in memslots is heavy since we need to walk all memeslots, it
can be reduced by this feature, and also avoid walking guest page table for
soft mmu.
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 1319050..e69a47a 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -197,6 +197,41 @@ static u64 __read_mostly shadow_x_mask; /* mutual exclusive with nx_mask */
static u64 __read_mostly shadow_user_mask;
static u64 __read_mostly shadow_accessed_mask;
static u64 __read_mostly shadow_dirty_mask;
+static u64 __read_mostly shadow_mmio_mask = (0xffull<< 49 | 1ULL);
One bit is shifted out. And it will fail with 52-bit MAXPHYADDR.
Please in addition, set the xwr bits to an invalid pattern on EPT (there
is an MSR which specifies which patterns are valid; for example
execute-only or write-only are invalid). If all patterns are valid AND
MAXPHYADDR == 52, then just set the mask to 0 and it the optimization
will be disabled.
--
error compiling committee.c: too many arguments to function
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