Re: [PATCH] BGRT: Don't ioremap if image address is in System RAM(was: Re: BGRT Pointer in System RAM)

[Andy Lutomirski]

On Tue, Jul 16, 2013 at 3:15 PM, Parag Warudkar <parag.lkml@xxxxxxxxx> wrote:
> On Mon, Jul 15, 2013 at 8:00 PM, Parag Warudkar <parag.lkml@xxxxxxxxx> wrote:
>> On Mon, Jul 15, 2013 at 7:56 PM, Parag Warudkar <parag.lkml@xxxxxxxxx> wrote:
>>> On Mon, Jul 15, 2013 at 7:04 PM, Josh Triplett <josh@xxxxxxxxxxxxxxxx> wrote:
>>>
>>>> We do need to handle the case of a valid pointer into memory that e820
>>>> calls system RAM, as well as the case of a valid pointer into memory
>>>> reserved for the BIOS or similar, but not the case of an invalid
>>>> pointer.
>>>
>>> Would that be as simple as
>>>
>>>                      page_is_ram(
>>
>> Damn shortcuts -
>>                         virt_addr = phys_to_virt(image->base_address);
>>                         if(page_is_ram(virt_to_page(virt_addr))) {
>>                             //direct read from virt addr
>>                         }
>>
>> Would that suffice for the System RAM case or some other MM trickery
>> is involved?
>
> Ok, so I played around with it a bit and the following patch works
> fine on my system. (I.E. image size is reasonable, cat
> /sys/firmware/acpi/bgrt/image > img.bmp generates a valid,
> non-distorted bitmap, which it did before too, btw as despite of the
> ioremap WARN_ON the ioremap seems to succeed if !(is_ram &&
> pfn_valid(pfn) && !PageReserved.)
>

How reliable is this?  That is, is there any guarantee that nothing
will have overwritten the image in memory before this code runs?

--Andy
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