On Tue, Oct 28, 2014 at 05:08:29PM +0000, Ard Biesheuvel wrote:
> On 28 October 2014 17:47, Mark Rutland <mark.rutland@xxxxxxx> wrote:
> > On Tue, Oct 28, 2014 at 04:18:37PM +0000, Ard Biesheuvel wrote:
> >> Instead of reserving the memory regions based on which types we know
> >> need to be reserved, consider only regions of the following types as
> >> free for general use by the OS:
> >>
> >> EFI_LOADER_CODE
> >> EFI_LOADER_DATA
> >> EFI_BOOT_SERVICES_CODE
> >> EFI_BOOT_SERVICES_DATA
> >> EFI_CONVENTIONAL_MEMORY
> >>
> >> Note that this also fixes a problem with the original code, which would
> >> misidentify a EFI_RUNTIME_SERVICES_DATA region as not reserved if it
> >> does not have the EFI_MEMORY_RUNTIME attribute set. However, it is
> >> perfectly legal for the firmware not to request a virtual mapping for
> >> EFI_RUNTIME_SERVICES_DATA regions that contain configuration tables, in
> >> which case the EFI_MEMORY_RUNTIME attribute would not be set.
> >>
> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> >> ---
> >> arch/arm64/kernel/efi.c | 20 ++++++++++----------
> >> 1 file changed, 10 insertions(+), 10 deletions(-)
> >>
> >> diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
> >> index 95c49ebc660d..2e829148fb36 100644
> >> --- a/arch/arm64/kernel/efi.c
> >> +++ b/arch/arm64/kernel/efi.c
> >> @@ -125,17 +125,17 @@ out:
> >> */
> >> static __init int is_reserve_region(efi_memory_desc_t *md)
> >> {
> >> - if (!is_normal_ram(md))
> >> + switch (md->type) {
> >> + case EFI_LOADER_CODE:
> >> + case EFI_LOADER_DATA:
> >> + case EFI_BOOT_SERVICES_CODE:
> >> + case EFI_BOOT_SERVICES_DATA:
> >> + case EFI_CONVENTIONAL_MEMORY:
> >> return 0;
> >> -
> >> - if (md->attribute & EFI_MEMORY_RUNTIME)
> >> - return 1;
> >> -
> >> - if (md->type == EFI_ACPI_RECLAIM_MEMORY ||
> >> - md->type == EFI_RESERVED_TYPE)
> >> - return 1;
> >> -
> >> - return 0;
> >> + default:
> >> + break;
> >> + }
> >> + return is_normal_ram(md);
> >
> > Just to check: did we figure out if UnusableMemory was allowed to have
> > EFI_MEMORY_WB attributes? If it isn't, this looks fine to me.
> >
> > If it is, then we will need to remove that memory (rather than reserving
> > it) to prevent speculative accesses.
> >
>
> The spec does not mention at all how EfiUnusableMemory should be used,
> and I would assume any such regions to have the EFI_MEMORY_WB
> attribute set, as it is carved out of the normal system RAM, and the
> way Tianocore/EDK2 implements it at least, all those attributes
> (including the write-protect/execute-protect ones) are copied straight
> from the underlying regions and never set to reflect the nature of the
> actual contents.
Ok. That's precisely the case I was concerned about.
> However, for 3.20 I intend to propose another change to this code, so
> that only non-reserved, usable memory gets memblock_add()'ed in the
> first place, and I suppose this should cover your concern as well. The
> reason for doing that is to allow tools like dmidecode and lshw access
> to the SMBIOS and other tables through /dev/mem, which is currently
> disallowed when STRICT_DEVMEM is set.
So long as said memory is not later passed to memblock_reserve, that
should be ok for the EfiUnusableMemory case. I guess we haven't actually
seen such memory yet anyhow?
I not all that keen on the usage of /dev/mem for those given the
availability of other interfaces.
Mark.
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