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powerpc/powernv: Fix vma page prot flags in opal-prd driver

PATCH RESEND Applied Vaidyanathan Srinivasan 3 participants 3 messages Jun 29, 2015 – Jul 7, 2015 PowerPC

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Vaidyanathan Srinivasan

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#0 lore raw

PATCH RESEND 1/1 powerpc/powernv: Fix vma page prot flags in opal-prd driver

opal-prd driver will mmap() firmware code/data area as private mapping to prd user space daemon. Write to this page will trigger COW faults. The new COW pages are normal kernel RAM pages accounted by the kernel and are not special.

vma->vm_page_prot value will be used at page fault time for the new COW pages, while pgprot_t value passed in remap_pfn_range() is used for the initial page table entry.

Hence:
* Do not add _PAGE_SPECIAL in vma, but only for remap_pfn_range()
* Also remap_pfn_range() will add the _PAGE_SPECIAL flag using pte_mkspecial() call, hence no need to specify in the driver

This fix resolves the page accounting warning shown below:

BUG: Bad rss-counter state mm:c0000007d34ac600 idx:1 val:19

The above warning is triggered since _PAGE_SPECIAL was incorrectly being set for the normal kernel COW pages.

Signed-off-by Vaidyanathan Srinivasan <[email protected]>
---
 arch/powerpc/platforms/powernv/opal-prd.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

Resending the patch for inclusion until we have a working solution without PAGE_SPECIAL.

Kindly queue this patch to fix the mmap issue in opal-prd driver. The next version/fix with vm_insert_page() will replace this code. There is no API change on the driver side and hence no side effects of including this fix until a better solution is available.

arch/powerpc/platforms/powernv/opal-prd.c +4 -5
index 46cb3fe..4ece8e4 100644
@@ -112,6 +112,7 @@ static int opal_prd_open(struct inode *inode, struct file *file)
 static int opal_prd_mmap(struct file *file, struct vm_area_struct *vma)
 {
 	size_t addr, size;
+	pgprot_t page_prot;
 	int rc;
 
 	pr_devel("opal_prd_mmap(0x%016lx, 0x%016lx, 0x%lx, 0x%lx)\n",

@@ -125,13 +126,11 @@ static int opal_prd_mmap(struct file *file, struct vm_area_struct *vma)
 	if (!opal_prd_range_is_valid(addr, size))
 		return -EINVAL;
 
-	vma->vm_page_prot = __pgprot(pgprot_val(phys_mem_access_prot(file,
-						vma->vm_pgoff,
-						 size, vma->vm_page_prot))
-					| _PAGE_SPECIAL);
+	page_prot = phys_mem_access_prot(file, vma->vm_pgoff,
+					 size, vma->vm_page_prot);
 
 	rc = remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff, size,
-			vma->vm_page_prot);
+				page_prot);
 
 	return rc;
 }
Acked-by on v1 1/1
#1 lore raw

Hi Vaidy,

Quoted 14 lines

opal-prd driver will mmap() firmware code/data area as private mapping to prd user space daemon. Write to this page will trigger COW faults. The new COW pages are normal kernel RAM pages accounted by the kernel and are not special.

vma->vm_page_prot value will be used at page fault time for the new COW pages, while pgprot_t value passed in remap_pfn_range() is used for the initial page table entry.

Hence:
* Do not add _PAGE_SPECIAL in vma, but only for remap_pfn_range()
* Also remap_pfn_range() will add the _PAGE_SPECIAL flag using pte_mkspecial() call, hence no need to specify in the driver

Quoted 7 lines

This fix resolves the page accounting warning shown below:

BUG: Bad rss-counter state mm:c0000007d34ac600 idx:1 val:19

The above warning is triggered since _PAGE_SPECIAL was incorrectly being set for the normal kernel COW pages.

Signed-off-by Vaidyanathan Srinivasan <[email protected]>
Acked-by Jeremy Kerr <[email protected]>

Cheers,

Jeremy

reviewer Applied
#2 lore raw
In reply to Vaidyanathan Srinivasan
Quoted 14 lines · Vaidyanathan Srinivasan

opal-prd driver will mmap() firmware code/data area as private mapping to prd user space daemon. Write to this page will trigger COW faults. The new COW pages are normal kernel RAM pages accounted by the kernel and are not special.

vma->vm_page_prot value will be used at page fault time for the new COW pages, while pgprot_t value passed in remap_pfn_range() is used for the initial page table entry.

Hence:
* Do not add _PAGE_SPECIAL in vma, but only for remap_pfn_range()
* Also remap_pfn_range() will add the _PAGE_SPECIAL flag using pte_mkspecial() call, hence no need to specify in the driver

Quoted 8 lines

This fix resolves the page accounting warning shown below:

BUG: Bad rss-counter state mm:c0000007d34ac600 idx:1 val:19

The above warning is triggered since _PAGE_SPECIAL was incorrectly being set for the normal kernel COW pages.

Signed-off-by Vaidyanathan Srinivasan <[email protected]>
Acked-by Jeremy Kerr <[email protected]>

Applied to powerpc fixes, thanks.

https://git.kernel.org/cgit/linux/kernel/git/powerpc/linux.git/commit/?h=fixes&id=d8ea782b56d9d2c46a47b3231cfd16ecfb538c60

cheers