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

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

On 11/25/21 11:42, Joao Martins wrote:
> On 11/24/21 19:10, Joao Martins wrote:
>> @@ -245,8 +251,6 @@ static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf,
>>  		rc = VM_FAULT_SIGBUS;
>>  	}
>>  
>> -	if (rc == VM_FAULT_NOPAGE)
>> -		dax_set_mapping(vmf, pfn, fault_size);
>>  	dax_read_unlock(id);
>>  
>>  	return rc;
>>
> This last chunk is going to spoof out a new warning because @fault_size in
> dev_dax_huge_fault stops being used after this patch.
> I've added below chunk for the next version (in addition to Christoph comments in
> patch 4):
> 

Re-attached as a replacement patch below scissors line.

As mentioned earlier, I'll be respinning v7 series with the comments I got on patch 4 and
this replacement below. But given the build warning yesterday&today, figured I
preemptively attach a replacement for it.

----->8-----

From 2f4cb25c0a6546a27ced4981f0963546f386caec Mon Sep 17 00:00:00 2001
From: Joao Martins <joao.m.martins@oracle.com>
Date: Tue, 23 Nov 2021 06:00:38 -0500
Subject: [PATCH] device-dax: set mapping prior to vmf_insert_pfn{,_pmd,pud}()

Normally, the @page mapping is set prior to inserting the page into a
page table entry. Make device-dax adhere to the same ordering, rather
than setting mapping after the PTE is inserted.

The address_space never changes and it is always associated with the
same inode and underlying pages. So, the page mapping is set once but
cleared when the struct pages are removed/freed (i.e. after
{devm_}memunmap_pages()).

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
---
 drivers/dax/device.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/dax/device.c b/drivers/dax/device.c
index 9c87927d4bc2..19a6b86486ce 100644
--- a/drivers/dax/device.c
+++ b/drivers/dax/device.c
@@ -121,6 +121,8 @@ static vm_fault_t __dev_dax_pte_fault(struct dev_dax *dev_dax,

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

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

@@ -161,6 +163,8 @@ static vm_fault_t __dev_dax_pmd_fault(struct dev_dax *dev_dax,

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

+	dax_set_mapping(vmf, *pfn, fault_size);
+
 	return vmf_insert_pfn_pmd(vmf, *pfn, vmf->flags & FAULT_FLAG_WRITE);
 }

@@ -203,6 +207,8 @@ static vm_fault_t __dev_dax_pud_fault(struct dev_dax *dev_dax,

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

+	dax_set_mapping(vmf, *pfn, fault_size);
+
 	return vmf_insert_pfn_pud(vmf, *pfn, vmf->flags & FAULT_FLAG_WRITE);
 }
 #else
@@ -217,7 +223,6 @@ static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf,
 		enum page_entry_size pe_size)
 {
 	struct file *filp = vmf->vma->vm_file;
-	unsigned long fault_size;
 	vm_fault_t rc = VM_FAULT_SIGBUS;
 	int id;
 	pfn_t pfn;
@@ -230,23 +235,18 @@ static vm_fault_t dev_dax_huge_fault(struct vm_fault *vmf,
 	id = dax_read_lock();
 	switch (pe_size) {
 	case PE_SIZE_PTE:
-		fault_size = PAGE_SIZE;
 		rc = __dev_dax_pte_fault(dev_dax, vmf, &pfn);
 		break;
 	case PE_SIZE_PMD:
-		fault_size = PMD_SIZE;
 		rc = __dev_dax_pmd_fault(dev_dax, vmf, &pfn);
 		break;
 	case PE_SIZE_PUD:
-		fault_size = PUD_SIZE;
 		rc = __dev_dax_pud_fault(dev_dax, vmf, &pfn);
 		break;
 	default:
 		rc = VM_FAULT_SIGBUS;
 	}

-	if (rc == VM_FAULT_NOPAGE)
-		dax_set_mapping(vmf, pfn, fault_size);
 	dax_read_unlock(id);

 	return rc;
-- 
2.17.2