Re: [PATCH] x86/efi-bgrt: Replace early_memremap() with memremap()

[Josh Triplett <josh@joshtriplett.org>]

On Mon, Dec 21, 2015 at 02:12:52PM +0000, Matt Fleming wrote:
> Môshe reported the following warning triggered on his machine since
> commit 50a0cb565246 ("x86/efi-bgrt: Fix kernel panic when mapping BGRT
> data"),
> 
>   [    0.026936] ------------[ cut here ]------------
>   [    0.026941] WARNING: CPU: 0 PID: 0 at mm/early_ioremap.c:137 __early_ioremap+0x102/0x1bb()
>   [    0.026941] Modules linked in:
>   [    0.026944] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.4.0-rc1 #2
>   [    0.026945] Hardware name: Dell Inc. XPS 13 9343/09K8G1, BIOS A05 07/14/2015
>   [    0.026946]  0000000000000000 900f03d5a116524d ffffffff81c03e60 ffffffff813a3fff
>   [    0.026948]  0000000000000000 ffffffff81c03e98 ffffffff810a0852 00000000d7b76000
>   [    0.026949]  0000000000000000 0000000000000001 0000000000000001 000000000000017c
>   [    0.026951] Call Trace:
>   [    0.026955]  [<ffffffff813a3fff>] dump_stack+0x44/0x55
>   [    0.026958]  [<ffffffff810a0852>] warn_slowpath_common+0x82/0xc0
>   [    0.026959]  [<ffffffff810a099a>] warn_slowpath_null+0x1a/0x20
>   [    0.026961]  [<ffffffff81d8c395>] __early_ioremap+0x102/0x1bb
>   [    0.026962]  [<ffffffff81d8c602>] early_memremap+0x13/0x15
>   [    0.026964]  [<ffffffff81d78361>] efi_bgrt_init+0x162/0x1ad
>   [    0.026966]  [<ffffffff81d778ec>] efi_late_init+0x9/0xb
>   [    0.026968]  [<ffffffff81d58ff5>] start_kernel+0x46f/0x49f
>   [    0.026970]  [<ffffffff81d58120>] ? early_idt_handler_array+0x120/0x120
>   [    0.026972]  [<ffffffff81d58339>] x86_64_start_reservations+0x2a/0x2c
>   [    0.026974]  [<ffffffff81d58485>] x86_64_start_kernel+0x14a/0x16d
>   [    0.026977] ---[ end trace f9b3812eb8e24c58 ]---
>   [    0.026978] efi_bgrt: Ignoring BGRT: failed to map image memory
> 
> early_memremap() has an upper limit on the size of mapping it can
> handle which is ~200KB. Clearly the BGRT image on Môshe's machine is
> much larger than that.
> 
> There's actually no reason to restrict ourselves to using the early_*
> version of memremap() - the ACPI BGRT driver is invoked late enough in
> boot that we can use the standard version, with the benefit that the
> late version allows mappings of arbitrary size.
> 
> Reported-by: Môshe van der Sterre <me@moshe.nl>
> Tested-by: Môshe van der Sterre <me@moshe.nl>
> Cc: Josh Triplett <josh@joshtriplett.org>
> Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>
> Cc: Borislav Petkov <bp@suse.de>
> Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>

Reviewed-by: Josh Triplett <josh@joshtriplett.org>

>  arch/x86/platform/efi/efi-bgrt.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/platform/efi/efi-bgrt.c b/arch/x86/platform/efi/efi-bgrt.c
> index bf51f4c02562..b0970661870a 100644
> --- a/arch/x86/platform/efi/efi-bgrt.c
> +++ b/arch/x86/platform/efi/efi-bgrt.c
> @@ -72,14 +72,14 @@ void __init efi_bgrt_init(void)
>  		return;
>  	}
>  
> -	image = early_memremap(bgrt_tab->image_address, sizeof(bmp_header));
> +	image = memremap(bgrt_tab->image_address, sizeof(bmp_header), MEMREMAP_WB);
>  	if (!image) {
>  		pr_err("Ignoring BGRT: failed to map image header memory\n");
>  		return;
>  	}
>  
>  	memcpy(&bmp_header, image, sizeof(bmp_header));
> -	early_memunmap(image, sizeof(bmp_header));
> +	memunmap(image);
>  	bgrt_image_size = bmp_header.size;
>  
>  	bgrt_image = kmalloc(bgrt_image_size, GFP_KERNEL | __GFP_NOWARN);
> @@ -89,7 +89,7 @@ void __init efi_bgrt_init(void)
>  		return;
>  	}
>  
> -	image = early_memremap(bgrt_tab->image_address, bmp_header.size);
> +	image = memremap(bgrt_tab->image_address, bmp_header.size, MEMREMAP_WB);
>  	if (!image) {
>  		pr_err("Ignoring BGRT: failed to map image memory\n");
>  		kfree(bgrt_image);
> @@ -98,5 +98,5 @@ void __init efi_bgrt_init(void)
>  	}
>  
>  	memcpy(bgrt_image, image, bgrt_image_size);
> -	early_memunmap(image, bmp_header.size);
> +	memunmap(image);
>  }
> -- 
> 2.6.2
>