[PATCH] cxl: Fix memory page not handled

[PATCH] cxl: Fix memory page not handled

[Christophe Lombard]

The a in-kernel 'library' API can be called by drivers to help
interaction with an IBM XSL on a POWER9 system.

The cxllib_handle_fault() API is used to handle memory fault. All memory
pages of the specified buffer have to be handled but the last page is
never touched, and the address the adapter is trying to access is never
sent to the kernel for resolution.

This patch updates the loop on the memory pages to be handled.

Signed-off-by: Christophe Lombard <clombard@linux.vnet.ibm.com>

Fixes: 3ced8d730063 ("cxl: Export library to support IBM XSL");
---
 drivers/misc/cxl/cxllib.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/drivers/misc/cxl/cxllib.c b/drivers/misc/cxl/cxllib.c
index 5dba23c..0c1eaf0 100644
--- a/drivers/misc/cxl/cxllib.c
+++ b/drivers/misc/cxl/cxllib.c
@@ -219,8 +219,17 @@ int cxllib_handle_fault(struct mm_struct *mm, u64 addr, u64 size, u64 flags)
 
 	down_read(&mm->mmap_sem);
 
-	for (dar = addr; dar < addr + size; dar += page_size) {
-		if (!vma || dar < vma->vm_start || dar > vma->vm_end) {
+	vma = find_vma(mm, addr);
+	if (!vma) {
+		pr_err("Can't find vma for addr %016llx\n", addr);
+		rc = -EFAULT;
+		goto out;
+	}
+	/* get the size of the pages allocated */
+	page_size = vma_kernel_pagesize(vma);
+
+	for (dar = (addr & ~(page_size - 1)); dar <= (addr + size); dar += page_size) {
+		if (dar < vma->vm_start || dar > vma->vm_end) {
 			vma = find_vma(mm, addr);
 			if (!vma) {
 				pr_err("Can't find vma for addr %016llx\n", addr);
-- 
2.7.4

Re: [PATCH] cxl: Fix memory page not handled

[Frederic Barrat]

Le 22/09/2017 à 15:08, Christophe Lombard a écrit :
> The a in-kernel 'library' API can be called by drivers to help


"the in-kernel library"



> interaction with an IBM XSL on a POWER9 system.
> 
> The cxllib_handle_fault() API is used to handle memory fault. All memory
> pages of the specified buffer have to be handled but the last page is
> never touched, and the address the adapter is trying to access is never

nitpick: "never touched"? I thought it could be. It all depends on the 
input parameter. But it doesn't really matter, there's a bug.


> sent to the kernel for resolution.
> 
> This patch updates the loop on the memory pages to be handled.
> 
> Signed-off-by: Christophe Lombard <clombard@linux.vnet.ibm.com>
> 
> Fixes: 3ced8d730063 ("cxl: Export library to support IBM XSL");
> ---
>   drivers/misc/cxl/cxllib.c | 13 +++++++++++--
>   1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/misc/cxl/cxllib.c b/drivers/misc/cxl/cxllib.c
> index 5dba23c..0c1eaf0 100644
> --- a/drivers/misc/cxl/cxllib.c
> +++ b/drivers/misc/cxl/cxllib.c
> @@ -219,8 +219,17 @@ int cxllib_handle_fault(struct mm_struct *mm, u64 addr, u64 size, u64 flags)
> 
>   	down_read(&mm->mmap_sem);
> 
> -	for (dar = addr; dar < addr + size; dar += page_size) {
> -		if (!vma || dar < vma->vm_start || dar > vma->vm_end) {
> +	vma = find_vma(mm, addr);
> +	if (!vma) {
> +		pr_err("Can't find vma for addr %016llx\n", addr);
> +		rc = -EFAULT;
> +		goto out;
> +	}
> +	/* get the size of the pages allocated */
> +	page_size = vma_kernel_pagesize(vma);
> +
> +	for (dar = (addr & ~(page_size - 1)); dar <= (addr + size); dar += page_size) {


The end boundary should be 'dar < (addr + size)', or we may hit an extra 
page, which could fail (and cause the call to return an error). Thanks 
to John for spotting it!

   Fred


> +		if (dar < vma->vm_start || dar > vma->vm_end) {
>   			vma = find_vma(mm, addr);
>   			if (!vma) {
>   				pr_err("Can't find vma for addr %016llx\n", addr);
>