On 7 December 2015 at 13:26, Catalin Marinas <catalin.marinas at arm.com> wrote:
> On Mon, Nov 16, 2015 at 12:23:16PM +0100, Ard Biesheuvel wrote:
>> diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
>> index 23cfc08fc8ba..d3e4b5d6a8d2 100644
>> --- a/arch/arm64/kernel/head.S
>> +++ b/arch/arm64/kernel/head.S
> [...]
>> @@ -210,7 +210,15 @@ section_table:
>> ENTRY(stext)
>> bl preserve_boot_args
>> bl el2_setup // Drop to EL1, w20=cpu_boot_mode
>> - adrp x24, __PHYS_OFFSET
>> +
>> + /*
>> + * Before the linear mapping has been set up, __va() translations will
>> + * not produce usable virtual addresses unless we tweak PHYS_OFFSET to
>> + * compensate for the offset between the kernel mapping and the base of
>> + * the linear mapping. We will undo this in map_mem().
>> + */
>
> Minor typo in comment: I guess you meant "__pa() translations will not
> produce usable...".
>
No, not quite. __va() translations will normally produce addresses in
the linear mapping, which will not be set up when we first start using
it in create_mapping(). So until that time, we have to redirect __va()
translations into the kernel mapping, where swapper_pg_dir is
shadowed. I am hoping that Mark's planned changes to create_mapping()
will make this unnecessary, but I haven't seen any of his code yet.
As far as __pa() is concerned, that translation is actually tweaked so
it will always produce usable addresses, regardless of whether the
bias is still set or not. The reason is that va-to-pa translations are
always unambiguous.
>> diff --git a/arch/arm64/mm/dump.c b/arch/arm64/mm/dump.c
>> index 5a22a119a74c..f6272f450688 100644
>> --- a/arch/arm64/mm/dump.c
>> +++ b/arch/arm64/mm/dump.c
>> @@ -63,7 +63,8 @@ static struct addr_marker address_markers[] = {
>> { PCI_IO_END, "PCI I/O end" },
>> { MODULES_VADDR, "Modules start" },
>> { MODULES_END, "Modules end" },
>> - { PAGE_OFFSET, "Kernel Mapping" },
>> + { KIMAGE_VADDR, "Kernel Mapping" },
>> + { PAGE_OFFSET, "Linear Mapping" },
>> { -1, NULL },
>> };
>
> Apart from this, please change the pr_notice() in mem_init() to show the
> linear mapping at the end (keep them in ascending order).
>
OK