Re: [PATCH v2 1/3] arm64: spin-table: handle unmapped cpu-release-addrs

[Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

On 30 July 2014 14:00, Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org> wrote:
> On 30 July 2014 13:30, Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org> wrote:
>> On Wed, Jul 30, 2014 at 11:59:02AM +0100, Ard Biesheuvel wrote:
>>> From: Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>
>>>
>>> In certain cases the cpu-release-addr of a CPU may not fall in the
>>> linear mapping (e.g. when the kernel is loaded above this address due to
>>> the presence of other images in memory). This is problematic for the
>>> spin-table code as it assumes that it can trivially convert a
>>> cpu-release-addr to a valid VA in the linear map.
>>>
>>> This patch modifies the spin-table code to use a temporary cached
>>> mapping to write to a given cpu-release-addr, enabling us to support
>>> addresses regardless of whether they are covered by the linear mapping.
>>>
>>> Signed-off-by: Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>
>>> Tested-by: Mark Salter <msalter-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
>>> [ardb: added (__force void *) cast]
>>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
>>> ---
>>>  arch/arm64/kernel/smp_spin_table.c | 22 +++++++++++++++++-----
>>>  1 file changed, 17 insertions(+), 5 deletions(-)
>>
>> I'm nervous about this. What if the spin table sits in the same physical 64k
>> frame as a read-sensitive device and we're running with 64k pages?
>>
>
> I see what you mean. This is potentially hairy, as EFI already
> ioremap_cache()s everything known to it as normal DRAM, so using plain

Clarification: every Runtime Services region known to it as being
normal DRAM, which may cover this area

> ioremap() here if pfn_valid() returns false for cpu-release-addr's PFN
> may still result in mappings with different attributes for the same
> region. So how should we decide whether to call ioremap() or
> ioremap_cache() in this case?
>
> --
> Ard.