[PATCH v2] mm: remove unnecessary __get_user_pages_unlocked() calls

Lorenzo Stoakes
2016-10-26T09:25:58Z

In hva_to_pfn_slow() we are able to replace __get_user_pages_unlocked() with
get_user_pages_unlocked() since we can now pass gup_flags.

In async_pf_execute() we need to pass different tsk, mm arguments so
get_user_pages_remote() is the sane replacement here (having added manual
acquisition and release of mmap_sem.)

Since we pass a NULL pages parameter the subsequent call to
__get_user_pages_locked() will have previously bailed any attempt at
VM_FAULT_RETRY, so we do not change this behaviour by using
get_user_pages_remote() which does not invoke VM_FAULT_RETRY logic at all.

Additionally get_user_pages_remote() reintroduces use of the FOLL_TOUCH
flag. However, this flag was originally silently dropped by 1e9877902dc7e
("mm/gup: Introduce get_user_pages_remote()"), so this appears to have been
unintentional and reintroducing it is therefore not an issue.

Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
---
v2: update description to reference dropped FOLL_TOUCH flag

virt/kvm/async_pf.c | 7 ++++---
virt/kvm/kvm_main.c | 5 ++---
2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index 8035cc1..e8c832c 100644
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -82,10 +82,11 @@ static void async_pf_execute(struct work_struct *work)
/*
* This work is run asynchromously to the task which owns
* mm and might be done in another context, so we must
- * use FOLL_REMOTE.
+ * access remotely.
*/
- __get_user_pages_unlocked(NULL, mm, addr, 1, NULL,
- FOLL_WRITE | FOLL_REMOTE);
+ down_read(&mm->mmap_sem);
+ get_user_pages_remote(NULL, mm, addr, 1, FOLL_WRITE, NULL, NULL);
+ up_read(&mm->mmap_sem);

kvm_async_page_present_sync(vcpu, apf);

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 2907b7b..c45d951 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1415,13 +1415,12 @@ static int hva_to_pfn_slow(unsigned long addr, bool *async, bool write_fault,
npages = get_user_page_nowait(addr, write_fault, page);
up_read(&current->mm->mmap_sem);
} else {
- unsigned int flags = FOLL_TOUCH | FOLL_HWPOISON;
+ unsigned int flags = FOLL_HWPOISON;

if (write_fault)
flags |= FOLL_WRITE;

- npages = __get_user_pages_unlocked(current, current->mm, addr, 1,
- page, flags);
+ npages = get_user_pages_unlocked(addr, 1, page, flags);
}
if (npages != 1)
return npages;
--
2.10.1