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

[Frederic Barrat <fbarrat@linux.vnet.ibm.com>]

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);
>