Re: [PATCH v2 bpf-next 2/3] mm, xen: Separate xen use cases from ioremap.

[Mike Rapoport <rppt@kernel.org>]

On Fri, Feb 23, 2024 at 03:57:27PM -0800, Alexei Starovoitov wrote:
> From: Alexei Starovoitov <ast@kernel.org>
> 
> xen grant table and xenbus ring are not ioremap the way arch specific code is using it,
> so let's add VM_XEN flag to separate them from VM_IOREMAP users.
> xen will not and should not be calling ioremap_page_range() on that range.
> /proc/vmallocinfo will print such region as "xen" instead of "ioremap" as well.
> 
> Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> ---
>  arch/x86/xen/grant-table.c         | 2 +-
>  drivers/xen/xenbus/xenbus_client.c | 2 +-
>  include/linux/vmalloc.h            | 1 +
>  mm/vmalloc.c                       | 7 +++++--
>  4 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/xen/grant-table.c b/arch/x86/xen/grant-table.c
> index 1e681bf62561..b816db0349c4 100644
> --- a/arch/x86/xen/grant-table.c
> +++ b/arch/x86/xen/grant-table.c
> @@ -104,7 +104,7 @@ static int arch_gnttab_valloc(struct gnttab_vm_area *area, unsigned nr_frames)
>  	area->ptes = kmalloc_array(nr_frames, sizeof(*area->ptes), GFP_KERNEL);
>  	if (area->ptes == NULL)
>  		return -ENOMEM;
> -	area->area = get_vm_area(PAGE_SIZE * nr_frames, VM_IOREMAP);
> +	area->area = get_vm_area(PAGE_SIZE * nr_frames, VM_XEN);
>  	if (!area->area)
>  		goto out_free_ptes;
>  	if (apply_to_page_range(&init_mm, (unsigned long)area->area->addr,
> diff --git a/drivers/xen/xenbus/xenbus_client.c b/drivers/xen/xenbus/xenbus_client.c
> index 32835b4b9bc5..b9c81a2d578b 100644
> --- a/drivers/xen/xenbus/xenbus_client.c
> +++ b/drivers/xen/xenbus/xenbus_client.c
> @@ -758,7 +758,7 @@ static int xenbus_map_ring_pv(struct xenbus_device *dev,
>  	bool leaked = false;
>  	int err = -ENOMEM;
>  
> -	area = get_vm_area(XEN_PAGE_SIZE * nr_grefs, VM_IOREMAP);
> +	area = get_vm_area(XEN_PAGE_SIZE * nr_grefs, VM_XEN);
>  	if (!area)
>  		return -ENOMEM;
>  	if (apply_to_page_range(&init_mm, (unsigned long)area->addr,
> diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
> index c720be70c8dd..223e51c243bc 100644
> --- a/include/linux/vmalloc.h
> +++ b/include/linux/vmalloc.h
> @@ -28,6 +28,7 @@ struct iov_iter;		/* in uio.h */
>  #define VM_FLUSH_RESET_PERMS	0x00000100	/* reset direct map and flush TLB on unmap, can't be freed in atomic context */
>  #define VM_MAP_PUT_PAGES	0x00000200	/* put pages and free array in vfree */
>  #define VM_ALLOW_HUGE_VMAP	0x00000400      /* Allow for huge pages on archs with HAVE_ARCH_HUGE_VMALLOC */
> +#define VM_XEN			0x00000800	/* xen use cases */
>  
>  #if (defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)) && \
>  	!defined(CONFIG_KASAN_VMALLOC)

There's also VM_DEFER_KMEMLEAK a line below:

#if (defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)) && \
	!defined(CONFIG_KASAN_VMALLOC)
#define VM_DEFER_KMEMLEAK	0x00000801	/* defer kmemleak object creation */
#else
#define VM_DEFER_KMEMLEAK	0
#endif

It should be adjusted as well.
I think it makes sense to use an enumeration for vm_flags, just like as
Suren did for GFP
(https://lore.kernel.org/linux-mm/20240224015800.2569851-1-surenb@google.com/)

-- 
Sincerely yours,
Mike.