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Subject[PATCH 2/2] KVM: Enable async page fault processing.
Date
If asynchronous hva_to_pfn() is requested call GUP with FOLL_NOWAIT to
avoid sleeping on IO. Check for hwpoison is done at the same time,
otherwise check_user_page_hwpoison() will call GUP again and will put
vcpu to sleep.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
---
virt/kvm/kvm_main.c | 23 +++++++++++++++++++++--
1 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 74d032a..80f42ab 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1029,6 +1029,17 @@ static pfn_t get_fault_pfn(void)
return fault_pfn;
}

+int get_user_page_nowait(struct task_struct *tsk, struct mm_struct *mm,
+ unsigned long start, int write, struct page **page)
+{
+ int flags = FOLL_TOUCH | FOLL_NOWAIT | FOLL_HWPOISON | FOLL_GET;
+
+ if (write)
+ flags |= FOLL_WRITE;
+
+ return __get_user_pages(tsk, mm, start, 1, flags, page, NULL, NULL);
+}
+
static inline int check_user_page_hwpoison(unsigned long addr)
{
int rc, flags = FOLL_TOUCH | FOLL_HWPOISON | FOLL_WRITE;
@@ -1062,7 +1073,14 @@ static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long addr, bool atomic,
if (writable)
*writable = write_fault;

- npages = get_user_pages_fast(addr, 1, write_fault, page);
+ if (async) {
+ down_read(&current->mm->mmap_sem);
+ npages = get_user_page_nowait(current, current->mm,
+ addr, write_fault, page);
+ up_read(&current->mm->mmap_sem);
+ } else
+ npages = get_user_pages_fast(addr, 1, write_fault,
+ page);

/* map read fault as writable if possible */
if (unlikely(!write_fault) && npages == 1) {
@@ -1085,7 +1103,8 @@ static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long addr, bool atomic,
return get_fault_pfn();

down_read(&current->mm->mmap_sem);
- if (check_user_page_hwpoison(addr)) {
+ if (npages == -EHWPOISON ||
+ (!async && check_user_page_hwpoison(addr))) {
up_read(&current->mm->mmap_sem);
get_page(hwpoison_page);
return page_to_pfn(hwpoison_page);
--
1.7.1


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