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SubjectRe: [PATCH 2/2] KVM: Enable async page fault processing.
On Tue, Feb 01, 2011 at 01:21:47PM +0200, Gleb Natapov wrote:
> 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.
>
FOLL_NOWAIT is now in Linus tree, so this patch can be applied now. I
verified that it still applies and works.

> 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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--
Gleb.


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