From e57778a1e30470c9f5b79e370511b9af29b59c48 Mon Sep 17 00:00:00 2001 From: Jeremy Fitzhardinge Date: Mon, 16 Jun 2008 04:30:02 -0700 Subject: xen: implement ptep_modify_prot_start/commit Xen has a pte update function which will update a pte while preserving its accessed and dirty bits. This means that ptep_modify_prot_start() can be implemented as a simple read of the pte value. The hardware may update the pte in the meantime, but ptep_modify_prot_commit() updates it while preserving any changes that may have happened in the meantime. The updates in ptep_modify_prot_commit() are batched if we're currently in lazy mmu mode. The mmu_update hypercall can take a batch of updates to perform, but this code doesn't make particular use of that feature, in favour of using generic multicall batching to get them all into the hypervisor. The net effect of this is that each mprotect pte update turns from two expensive trap-and-emulate faults into they hypervisor into a single hypercall whose cost is amortized in a batched multicall. Signed-off-by: Jeremy Fitzhardinge Acked-by: Linus Torvalds Acked-by: Hugh Dickins Signed-off-by: Ingo Molnar --- include/xen/interface/features.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'include/xen/interface/features.h') diff --git a/include/xen/interface/features.h b/include/xen/interface/features.h index d73228d16488..f51b6413b054 100644 --- a/include/xen/interface/features.h +++ b/include/xen/interface/features.h @@ -38,6 +38,9 @@ */ #define XENFEAT_pae_pgdir_above_4gb 4 +/* x86: Does this Xen host support the MMU_PT_UPDATE_PRESERVE_AD hypercall? */ +#define XENFEAT_mmu_pt_update_preserve_ad 5 + #define XENFEAT_NR_SUBMAPS 1 #endif /* __XEN_PUBLIC_FEATURES_H__ */ -- cgit v1.2.3