Re: [PATCH v5 06/12] Add get_user_pages() variant that fails if major fault is required.

Avi Kivity
2010-08-23T15:52:09Z

On 07/19/2010 06:30 PM, Gleb Natapov wrote:
> This patch add get_user_pages() variant that only succeeds if getting
> a reference to a page doesn't require major fault.
>

Andrew, can this go in through kvm.git?

> Reviewed-by: Rik van Riel<riel@redhat.com>
> Signed-off-by: Gleb Natapov<gleb@redhat.com>
> ---
> fs/ncpfs/mmap.c | 2 ++
> include/linux/mm.h | 5 +++++
> mm/filemap.c | 3 +++
> mm/memory.c | 31 ++++++++++++++++++++++++++++---
> mm/shmem.c | 8 +++++++-
> 5 files changed, 45 insertions(+), 4 deletions(-)
>
> diff --git a/fs/ncpfs/mmap.c b/fs/ncpfs/mmap.c
> index 56f5b3a..b9c4f36 100644
> --- a/fs/ncpfs/mmap.c
> +++ b/fs/ncpfs/mmap.c
> @@ -39,6 +39,8 @@ static int ncp_file_mmap_fault(struct vm_area_struct *area,
> int bufsize;
> int pos; /* XXX: loff_t ? */
>
> + if (vmf->flags& FAULT_FLAG_MINOR)
> + return VM_FAULT_MAJOR | VM_FAULT_ERROR;
> /*
> * ncpfs has nothing against high pages as long
> * as recvmsg and memset works on it
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 4238a9c..2bfc85a 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -140,6 +140,7 @@ extern pgprot_t protection_map[16];
> #define FAULT_FLAG_WRITE 0x01 /* Fault was a write access */
> #define FAULT_FLAG_NONLINEAR 0x02 /* Fault was via a nonlinear mapping */
> #define FAULT_FLAG_MKWRITE 0x04 /* Fault was mkwrite of existing pte */
> +#define FAULT_FLAG_MINOR 0x08 /* Do only minor fault */
>
> /*
> * This interface is used by x86 PAT code to identify a pfn mapping that is
> @@ -843,6 +844,9 @@ extern int access_process_vm(struct task_struct *tsk, unsigned long addr, void *
> int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> unsigned long start, int nr_pages, int write, int force,
> struct page **pages, struct vm_area_struct **vmas);
> +int get_user_pages_noio(struct task_struct *tsk, struct mm_struct *mm,
> + unsigned long start, int nr_pages, int write, int force,
> + struct page **pages, struct vm_area_struct **vmas);
> int get_user_pages_fast(unsigned long start, int nr_pages, int write,
> struct page **pages);
> struct page *get_dump_page(unsigned long addr);
> @@ -1373,6 +1377,7 @@ struct page *follow_page(struct vm_area_struct *, unsigned long address,
> #define FOLL_GET 0x04 /* do get_page on page */
> #define FOLL_DUMP 0x08 /* give error on hole if it would be zero */
> #define FOLL_FORCE 0x10 /* get_user_pages read/write w/o permission */
> +#define FOLL_MINOR 0x20 /* do only minor page faults */
>
> typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
> void *data);
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 20e5642..1186338 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1548,6 +1548,9 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> goto no_cached_page;
> }
> } else {
> + if (vmf->flags& FAULT_FLAG_MINOR)
> + return VM_FAULT_MAJOR | VM_FAULT_ERROR;
> +
> /* No page in the page cache at all */
> do_sync_mmap_readahead(vma, ra, file, offset);
> count_vm_event(PGMAJFAULT);
> diff --git a/mm/memory.c b/mm/memory.c
> index 119b7cc..7dfaba2 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -1433,10 +1433,13 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> cond_resched();
> while (!(page = follow_page(vma, start, foll_flags))) {
> int ret;
> + unsigned int fault_fl =
> + ((foll_flags& FOLL_WRITE) ?
> + FAULT_FLAG_WRITE : 0) |
> + ((foll_flags& FOLL_MINOR) ?
> + FAULT_FLAG_MINOR : 0);
>
> - ret = handle_mm_fault(mm, vma, start,
> - (foll_flags& FOLL_WRITE) ?
> - FAULT_FLAG_WRITE : 0);
> + ret = handle_mm_fault(mm, vma, start, fault_fl);
>
> if (ret& VM_FAULT_ERROR) {
> if (ret& VM_FAULT_OOM)
> @@ -1444,6 +1447,8 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> if (ret&
> (VM_FAULT_HWPOISON|VM_FAULT_SIGBUS))
> return i ? i : -EFAULT;
> + else if (ret& VM_FAULT_MAJOR)
> + return i ? i : -EFAULT;
> BUG();
> }
> if (ret& VM_FAULT_MAJOR)
> @@ -1554,6 +1559,23 @@ int get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> }
> EXPORT_SYMBOL(get_user_pages);
>
> +int get_user_pages_noio(struct task_struct *tsk, struct mm_struct *mm,
> + unsigned long start, int nr_pages, int write, int force,
> + struct page **pages, struct vm_area_struct **vmas)
> +{
> + int flags = FOLL_TOUCH | FOLL_MINOR;
> +
> + if (pages)
> + flags |= FOLL_GET;
> + if (write)
> + flags |= FOLL_WRITE;
> + if (force)
> + flags |= FOLL_FORCE;
> +
> + return __get_user_pages(tsk, mm, start, nr_pages, flags, pages, vmas);
> +}
> +EXPORT_SYMBOL(get_user_pages_noio);
> +
> /**
> * get_dump_page() - pin user page in memory while writing it to core dump
> * @addr: user address
> @@ -2640,6 +2662,9 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
> delayacct_set_flag(DELAYACCT_PF_SWAPIN);
> page = lookup_swap_cache(entry);
> if (!page) {
> + if (flags& FAULT_FLAG_MINOR)
> + return VM_FAULT_MAJOR | VM_FAULT_ERROR;
> +
> grab_swap_token(mm); /* Contend for token _before_ read-in */
> page = swapin_readahead(entry,
> GFP_HIGHUSER_MOVABLE, vma, address);
> diff --git a/mm/shmem.c b/mm/shmem.c
> index f65f840..acc8958 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1227,6 +1227,7 @@ static int shmem_getpage(struct inode *inode, unsigned long idx,
> swp_entry_t swap;
> gfp_t gfp;
> int error;
> + int flags = type ? *type : 0;
>
> if (idx>= SHMEM_MAX_INDEX)
> return -EFBIG;
> @@ -1275,6 +1276,11 @@ repeat:
> swappage = lookup_swap_cache(swap);
> if (!swappage) {
> shmem_swp_unmap(entry);
> + if (flags& FAULT_FLAG_MINOR) {
> + spin_unlock(&info->lock);
> + *type = VM_FAULT_MAJOR | VM_FAULT_ERROR;
> + goto failed;
> + }
> /* here we actually do the io */
> if (type&& !(*type& VM_FAULT_MAJOR)) {
> __count_vm_event(PGMAJFAULT);
> @@ -1483,7 +1489,7 @@ static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
> {
> struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
> int error;
> - int ret;
> + int ret = (int)vmf->flags;
>
> if (((loff_t)vmf->pgoff<< PAGE_CACHE_SHIFT)>= i_size_read(inode))
> return VM_FAULT_SIGBUS;

--
error compiling committee.c: too many arguments to function