Re: [PATCH v6 09/10] device-dax: set mapping prior to vmf_insert_pfn{,_pmd,pud}()

[Joao Martins <joao.m.martins@oracle.com>]

On 11/29/21 15:49, Joao Martins wrote:
> On 11/29/21 07:32, Christoph Hellwig wrote:
>> On Fri, Nov 26, 2021 at 06:39:39PM +0000, Joao Martins wrote:
>> Aso it seems like pfn is only an input
>> parameter now and doesn't need to be passed by reference.
>>
> It's actually just an output parameter (that dax_set_mapping would then use).
> 
> The fault handlers in device-dax use vmf->address to calculate pfn that they
> insert in the page table entry. After this patch we can actually just remove
> @pfn argument.

I've added your suggestion as a cleanup patch between 9 and current 10 (11 in v7):

---->8----

From 999cec9efa757b82f435124518b042caeb51bde6 Mon Sep 17 00:00:00 2001
From: Joao Martins <joao.m.martins@oracle.com>
Date: Mon, 29 Nov 2021 11:12:00 -0500
Subject: [PATCH] device-dax: remove pfn from __dev_dax_{pte,pmd,pud}_fault()

After moving the page mapping to be set prior to pte insertion, the pfn
in dev_dax_huge_fault() no longer is necessary.  Remove it, as well as
the @pfn argument passed to the internal fault handler helpers.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
---
 drivers/dax/device.c | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/drivers/dax/device.c b/drivers/dax/device.c
index 19a6b86486ce..914368164e05 100644
--- a/drivers/dax/device.c
+++ b/drivers/dax/device.c
@@ -95,10 +95,11 @@ static void dax_set_mapping(struct vm_fault *vmf, pfn_t pfn,
 }

 static vm_fault_t __dev_dax_pte_fault(struct dev_dax *dev_dax,
-                               struct vm_fault *vmf, pfn_t *pfn)
+                               struct vm_fault *vmf)
 {
        struct device *dev = &dev_dax->dev;
        phys_addr_t phys;
+       pfn_t pfn;
        unsigned int fault_size = PAGE_SIZE;

        if (check_vma(dev_dax, vmf->vma, __func__))
@@ -119,20 +120,21 @@ static vm_fault_t __dev_dax_pte_fault(struct dev_dax *dev_dax,
                return VM_FAULT_SIGBUS;
        }

-       *pfn = phys_to_pfn_t(phys, PFN_DEV|PFN_MAP);
+       pfn = phys_to_pfn_t(phys, PFN_DEV|PFN_MAP);

-       dax_set_mapping(vmf, *pfn, fault_size);
+       dax_set_mapping(vmf, pfn, fault_size);

-       return vmf_insert_mixed(vmf->vma, vmf->address, *pfn);
+       return vmf_insert_mixed(vmf->vma, vmf->address, pfn);
 }

 static vm_fault_t __dev_dax_pmd_fault(struct dev_dax *dev_dax,
-                               struct vm_fault *vmf, pfn_t *pfn)
+                               struct vm_fault *vmf)
 {
        unsigned long pmd_addr = vmf->address & PMD_MASK;
        struct device *dev = &dev_dax->dev;
        phys_addr_t phys;
        pgoff_t pgoff;
+       pfn_t pfn;
        unsigned int fault_size = PMD_SIZE;

        if (check_vma(dev_dax, vmf->vma, __func__))
@@ -161,21 +163,22 @@ static vm_fault_t __dev_dax_pmd_fault(struct dev_dax *dev_dax,
                return VM_FAULT_SIGBUS;
        }

-       *pfn = phys_to_pfn_t(phys, PFN_DEV|PFN_MAP);
+       pfn = phys_to_pfn_t(phys, PFN_DEV|PFN_MAP);

-       dax_set_mapping(vmf, *pfn, fault_size);
+       dax_set_mapping(vmf, pfn, fault_size);

-       return vmf_insert_pfn_pmd(vmf, *pfn, vmf->flags & FAULT_FLAG_WRITE);
+       return vmf_insert_pfn_pmd(vmf, pfn, vmf->flags & FAULT_FLAG_WRITE);
 }
 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 static vm_fault_t __dev_dax_pud_fault(struct dev_dax *dev_dax,
-                               struct vm_fault *vmf, pfn_t *pfn)
+                               struct vm_fault *vmf)
 {
        unsigned long pud_addr = vmf->address & PUD_MASK;
        struct device *dev = &dev_dax->dev;
        phys_addr_t phys;
        pgoff_t pgoff;
+       pfn_t pfn;
        unsigned int fault_size = PUD_SIZE;


@@ -205,11 +208,11 @@ static vm_fault_t __dev_dax_pud_fault(struct dev_dax *dev_dax,
                return VM_FAULT_SIGBUS;
        }

-       *pfn = phys_to_pfn_t(phys, PFN_DEV|PFN_MAP);
+       pfn = phys_to_pfn_t(phys, PFN_DEV|PFN_MAP);

-       dax_set_mapping(vmf, *pfn, fault_size);
+       dax_set_mapping(vmf, pfn, fault_size);

-       return vmf_insert_pfn_pud(vmf, *pfn, vmf->flags & FAULT_FLAG_WRITE);
+       return vmf_insert_pfn_pud(vmf, pfn, vmf->flags & FAULT_FLAG_WRITE);
 }
 #else
 static vm_fault_t __dev_dax_pud_fault(struct dev_dax *dev_dax,
@@ -225,7 +228,6 @@ static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf,
        struct file *filp = vmf->vma->vm_file;
        vm_fault_t rc = VM_FAULT_SIGBUS;
        int id;
-       pfn_t pfn;
        struct dev_dax *dev_dax = filp->private_data;

        dev_dbg(&dev_dax->dev, "%s: %s (%#lx - %#lx) size = %d\n", current->comm,
@@ -235,13 +237,13 @@ static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf,
        id = dax_read_lock();
        switch (pe_size) {
        case PE_SIZE_PTE:
-               rc = __dev_dax_pte_fault(dev_dax, vmf, &pfn);
+               rc = __dev_dax_pte_fault(dev_dax, vmf);
                break;
        case PE_SIZE_PMD:
-               rc = __dev_dax_pmd_fault(dev_dax, vmf, &pfn);
+               rc = __dev_dax_pmd_fault(dev_dax, vmf);
                break;
        case PE_SIZE_PUD:
-               rc = __dev_dax_pud_fault(dev_dax, vmf, &pfn);
+               rc = __dev_dax_pud_fault(dev_dax, vmf);
                break;
        default:
                rc = VM_FAULT_SIGBUS;
--
2.17.2