On Thu, 2014-07-31 at 11:04 +0100, Will Deacon wrote: > On Thu, Jul 31, 2014 at 10:58:54AM +0100, Mark Rutland wrote: > > On Thu, Jul 31, 2014 at 10:45:15AM +0100, Will Deacon wrote: > > > On Wed, Jul 30, 2014 at 08:17:02PM +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? > > > > > > > > > > > > > Actually, booting.txt requires cpu-release-addr to point to a > > > > /memreserve/d part of memory, which implies DRAM (or you wouldn't have > > > > to memreserve it) > > > > That means it should always be covered by the linear mapping, unless > > > > it is located before Image in DRAM, which is the case addressed by > > > > this patch. > > > > > > But if it's located before before the Image in DRAM and isn't covered by > > > the linear mapping, then surely the /memreserve/ is pointless too? In which > > > case, this looks like we're simply trying to cater for platforms that aren't > > > following booting.txt (which may need updating if we need to handle this). > > > > No. The DT is describing the memory which is present, and the subset > > thereof which should not be used under normal circumstances. That's a > > static property of the system. > > > > Where the OS happens to get loaded and what it is able to address is a > > dynamic property of the OS (and possibly the bootloader). The DT cannot > > have knowledge of this. > > > > It's always true that the OS should not blindly use memreserve'd memory. > > The fact that it cannot address it in the linear mapping is orthogonal. > > In which case, I think asserting that /memreserve/ implies DRAM is pretty > fragile and not actually enforced anywhere. Sure, we can say `don't do > that', but I'd prefer to have the kernel detect this dynamically. > > Does dtc check that the /memreserve/ region is actually a subset of the > memory node? The handling of /memreserve/ in drivers/of/fdt.c uses the memblock API to reserve. And that means it is assumed that /memreserve/ is something which can be covered by the normal kernel RAM mapping. I suspect having /memreserve/ outside the kernel mapping would cause problems for the mm code. -- 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
