On 03/08/17 at 02:30pm, Bhupesh Sharma wrote:
> Hi Dave,
>
> On Wed, Mar 8, 2017 at 1:48 PM, Dave Young <dyoung@xxxxxxxxxx> wrote:
> > On 03/08/17 at 03:47pm, Baoquan He wrote:
> >> - * We allocate runtime services regions bottom-up, starting from -4G, i.e.
> >> + * We allocate runtime services regions top-down, starting from -4G, i.e.
> >
> > Baoquan, I think original bottom-up is right, it is just considering
> > -68G as up, see the x86_64 mm.txt. We regard vmalloc as higher address
> > although from mathematics view it is lower then positive addresses.
>
> I think you have a valid point, but I think the -4G convention is
> probably too confusing to read and may lead to issues when we use this
> for future feature addition as well. It would be more useful to use
> the macros similar to the MODULES_{} addresses we use currently in
> 'arch/x86/include/asm/pgtable_64_types.h':
>
> #define MODULES_VADDR (__START_KERNEL_map + KERNEL_IMAGE_SIZE)
> #define MODULES_END _AC(0xffffffffff000000, UL)
> #define MODULES_LEN (MODULES_END - MODULES_VADDR)
>
> May be we can use the following convention for the EFI_VA_{} addresses
> as per 'http://lxr.free-electrons.com/source/Documentation/x86/x86_64/mm.txt#L19':
>
> #define EFI_VA_START _AC(0xfffffffeffffffff, UL)
> #define EFI_VA_END _AC(0xffffffef00000000, UL)
Isn't it like this:
#define EFI_VA_START _AC(0xffffffff00000000, UL)
#define EFI_VA_END _AC(0xffffffef00000000, UL)
Just make them be equal to value which computer stores -4G and -68G?
You can see in arch/x86/platform/efi/efi_64.c, it's using efi_va minus
size directly, here size should be 4K, page aligned.
efi_va -= size;
Above formula has considered the open interval attribute of
EFI_VA_START. Making EFI_VA_START be 0xfffffffeffffffff could be wrong.
Right?
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