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

[Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>]

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?

Will