The patch titled
KVM: MMU: Page table write flood protection
has been removed from the -mm tree. Its filename was
kvm-mmu-page-table-write-flood-protection.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
Subject: KVM: MMU: Page table write flood protection
From: Avi Kivity <avi@xxxxxxxxxxxx>
In fork() (or when we protect a page that is no longer a page table), we can
experience floods of writes to a page, which have to be emulated. This is
expensive.
So, if we detect such a flood, zap the page so subsequent writes can proceed
natively.
Signed-off-by: Avi Kivity <avi@xxxxxxxxxxxx>
Acked-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
drivers/kvm/kvm.h | 3 +++
drivers/kvm/mmu.c | 16 +++++++++++++++-
2 files changed, 18 insertions(+), 1 deletion(-)
diff -puN drivers/kvm/kvm.h~kvm-mmu-page-table-write-flood-protection drivers/kvm/kvm.h
--- a/drivers/kvm/kvm.h~kvm-mmu-page-table-write-flood-protection
+++ a/drivers/kvm/kvm.h
@@ -238,6 +238,9 @@ struct kvm_vcpu {
struct kvm_mmu_page page_header_buf[KVM_NUM_MMU_PAGES];
struct kvm_mmu mmu;
+ gfn_t last_pt_write_gfn;
+ int last_pt_write_count;
+
struct kvm_guest_debug guest_debug;
char fx_buf[FX_BUF_SIZE];
diff -puN drivers/kvm/mmu.c~kvm-mmu-page-table-write-flood-protection drivers/kvm/mmu.c
--- a/drivers/kvm/mmu.c~kvm-mmu-page-table-write-flood-protection
+++ a/drivers/kvm/mmu.c
@@ -969,8 +969,17 @@ void kvm_mmu_pre_write(struct kvm_vcpu *
unsigned page_offset;
unsigned misaligned;
int level;
+ int flooded = 0;
pgprintk("%s: gpa %llx bytes %d\n", __FUNCTION__, gpa, bytes);
+ if (gfn == vcpu->last_pt_write_gfn) {
+ ++vcpu->last_pt_write_count;
+ if (vcpu->last_pt_write_count >= 3)
+ flooded = 1;
+ } else {
+ vcpu->last_pt_write_gfn = gfn;
+ vcpu->last_pt_write_count = 1;
+ }
index = kvm_page_table_hashfn(gfn) % KVM_NUM_MMU_PAGES;
bucket = &vcpu->kvm->mmu_page_hash[index];
hlist_for_each_entry_safe(page, node, n, bucket, hash_link) {
@@ -978,11 +987,16 @@ void kvm_mmu_pre_write(struct kvm_vcpu *
continue;
pte_size = page->role.glevels == PT32_ROOT_LEVEL ? 4 : 8;
misaligned = (offset ^ (offset + bytes - 1)) & ~(pte_size - 1);
- if (misaligned) {
+ if (misaligned || flooded) {
/*
* Misaligned accesses are too much trouble to fix
* up; also, they usually indicate a page is not used
* as a page table.
+ *
+ * If we're seeing too many writes to a page,
+ * it may no longer be a page table, or we may be
+ * forking, in which case it is better to unmap the
+ * page.
*/
pgprintk("misaligned: gpa %llx bytes %d role %x\n",
gpa, bytes, page->role.word);
_
Patches currently in -mm which might be from avi@xxxxxxxxxxxx are
-
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