On Wed, Jul 30, 2014 at 01:42:58PM +0100, Will Deacon wrote: > On Wed, Jul 30, 2014 at 01:30:29PM +0100, Mark Rutland wrote: > > On Wed, Jul 30, 2014 at 01:00:40PM +0100, Ard Biesheuvel wrote: > > > On 30 July 2014 13:30, Will Deacon <will.deacon@xxxxxxx> wrote: > > > > On Wed, Jul 30, 2014 at 11:59:02AM +0100, Ard Biesheuvel wrote: > > > >> From: Mark Rutland <mark.rutland@xxxxxxx> > > > >> > > > >> 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@xxxxxxx> > > > >> Tested-by: Mark Salter <msalter@xxxxxxxxxx> > > > >> [ardb: added (__force void *) cast] > > > >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > > > >> --- > > > >> 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 > > > 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? > > > > If we're careful about handling mismatched attributes we might be able > > to get away with always using a device mapping. > > Even then, I think ioremap hits a WARN_ON if pfn_valid. Ok, that's that idea dead then. > > I'll need to have a think about that, I'm not sure on the architected > > cache behaviour in such a case. > > Of we just skip the cache flush if !pfn_valid. I don't think that's always safe given Ard's comment that the EFI code will possibly have a mapping covering the region created by ioremap_cache. Ard, what exactly does the EFI code map with ioremap_cache, and why? Cheers, Mark. -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
