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Subject: Re: [PATCH 3/3] sgi-gru: Use __get_user_pages_fast in
 atomic_pte_lookup
To:     Bharath Vedartham <linux.bhar@gmail.com>
CC:     <arnd@arndb.de>, <sivanich@sgi.com>, <gregkh@linuxfoundation.org>,
        <ira.weiny@intel.com>, <jglisse@redhat.com>,
        <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>
References: <1563724685-6540-1-git-send-email-linux.bhar@gmail.com>
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 <c508330d-a5d0-fba3-9dd0-eb820a96ee09@nvidia.com>
 <20190722175310.GC12278@bharath12345-Inspiron-5559>
From:   John Hubbard <jhubbard@nvidia.com>
Message-ID: <15223dd3-8018-65f0-dc0b-aef43945e54e@nvidia.com>
Date:   Mon, 22 Jul 2019 16:06:09 -0700
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On 7/22/19 10:53 AM, Bharath Vedartham wrote:
> On Sun, Jul 21, 2019 at 07:32:36PM -0700, John Hubbard wrote:
>> On 7/21/19 8:58 AM, Bharath Vedartham wrote:
...

>> Also, optional: as long as you're there, atomic_pte_lookup() ought to
>> either return a bool (true == success) or an errno, rather than a
>> numeric zero or one.
> That makes sense. But the code which uses atomic_pte_lookup uses the
> return value of 1 for success and failure value of 0 in gru_vtop. That's
> why I did not mess with the return values in this code. It would require
> some change in the driver functionality which I am not ready to do :(

It's a static function with only one caller. You could just merge in
something like this, on top of what you have:

diff --git a/drivers/misc/sgi-gru/grufault.c b/drivers/misc/sgi-gru/grufault.c
index 121c9a4ccb94..2f768fc06432 100644
--- a/drivers/misc/sgi-gru/grufault.c
+++ b/drivers/misc/sgi-gru/grufault.c
@@ -189,10 +189,11 @@ static int non_atomic_pte_lookup(struct vm_area_struct *vma,
        return 0;
 }
 
-/*
- * atomic_pte_lookup
+/**
+ * atomic_pte_lookup() - Convert a user virtual address to a physical address
+ * @Return: true for success, false for failure. Failure means that the page
+ *         could not be pinned via gup fast.
  *
- * Convert a user virtual address to a physical address
  * Only supports Intel large pages (2MB only) on x86_64.
  *     ZZZ - hugepage support is incomplete
  *
@@ -207,12 +208,12 @@ static int atomic_pte_lookup(struct vm_area_struct *vma, unsigned long vaddr,
        *pageshift = is_vm_hugetlb_page(vma) ? HPAGE_SHIFT : PAGE_SHIFT;
 
        if (!__get_user_pages_fast(vaddr, 1, write, &page))
-               return 1;
+               return false;
 
        *paddr = page_to_phys(page);
        put_user_page(page);
 
-       return 0;
+       return true;
 }
 
 static int gru_vtop(struct gru_thread_state *gts, unsigned long vaddr,
@@ -221,7 +222,8 @@ static int gru_vtop(struct gru_thread_state *gts, unsigned long vaddr,
        struct mm_struct *mm = gts->ts_mm;
        struct vm_area_struct *vma;
        unsigned long paddr;
-       int ret, ps;
+       int ps;
+       bool success;
 
        vma = find_vma(mm, vaddr);
        if (!vma)
@@ -232,8 +234,8 @@ static int gru_vtop(struct gru_thread_state *gts, unsigned long vaddr,
         * context.
         */
        rmb();  /* Must/check ms_range_active before loading PTEs */
-       ret = atomic_pte_lookup(vma, vaddr, write, &paddr, &ps);
-       if (ret) {
+       success = atomic_pte_lookup(vma, vaddr, write, &paddr, &ps);
+       if (!success) {
                if (atomic)
                        goto upm;
                if (non_atomic_pte_lookup(vma, vaddr, write, &paddr, &ps))


thanks,
-- 
John Hubbard
NVIDIA