On Fri, 31 May 2019 at 01:13, Dan Williams <[email protected]> wrote: > > UEFI 2.8 defines an EFI_MEMORY_SP attribute bit to augment the > interpretation of the EFI Memory Types as "reserved for a specific > purpose". The intent of this bit is to allow the OS to identify precious > or scarce memory resources and optionally manage it separately from > EfiConventionalMemory. As defined older OSes that do not know about this > attribute are permitted to ignore it and the memory will be handled > according to the OS default policy for the given memory type. > > In other words, this "specific purpose" hint is deliberately weaker than > EfiReservedMemoryType in that the system continues to operate if the OS > takes no action on the attribute. The risk of taking no action is > potentially unwanted / unmovable kernel allocations from the designated > resource that prevent the full realization of the "specific purpose". > For example, consider a system with a high-bandwidth memory pool. Older > kernels are permitted to boot and consume that memory as conventional > "System-RAM" newer kernels may arrange for that memory to be set aside > by the system administrator for a dedicated high-bandwidth memory aware > application to consume. > > Specifically, this mechanism allows for the elimination of scenarios > where platform firmware tries to game OS policy by lying about ACPI SLIT > values, i.e. claiming that a precious memory resource has a high > distance to trigger the OS to avoid it by default. > > Implement simple detection of the bit for EFI memory table dumps and > save the kernel policy for a follow-on change. > > Cc: Ard Biesheuvel <[email protected]> > Signed-off-by: Dan Williams <[email protected]>
Reviewed-by: Ard Biesheuvel <[email protected]> > --- > drivers/firmware/efi/efi.c | 5 +++-- > include/linux/efi.h | 1 + > 2 files changed, 4 insertions(+), 2 deletions(-) > > diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c > index 55b77c576c42..81db09485881 100644 > --- a/drivers/firmware/efi/efi.c > +++ b/drivers/firmware/efi/efi.c > @@ -848,15 +848,16 @@ char * __init efi_md_typeattr_format(char *buf, size_t > size, > if (attr & ~(EFI_MEMORY_UC | EFI_MEMORY_WC | EFI_MEMORY_WT | > EFI_MEMORY_WB | EFI_MEMORY_UCE | EFI_MEMORY_RO | > EFI_MEMORY_WP | EFI_MEMORY_RP | EFI_MEMORY_XP | > - EFI_MEMORY_NV | > + EFI_MEMORY_NV | EFI_MEMORY_SP | > EFI_MEMORY_RUNTIME | EFI_MEMORY_MORE_RELIABLE)) > snprintf(pos, size, "|attr=0x%016llx]", > (unsigned long long)attr); > else > snprintf(pos, size, > - "|%3s|%2s|%2s|%2s|%2s|%2s|%2s|%3s|%2s|%2s|%2s|%2s]", > + > "|%3s|%2s|%2s|%2s|%2s|%2s|%2s|%2s|%3s|%2s|%2s|%2s|%2s]", > attr & EFI_MEMORY_RUNTIME ? "RUN" : "", > attr & EFI_MEMORY_MORE_RELIABLE ? "MR" : "", > + attr & EFI_MEMORY_SP ? "SP" : "", > attr & EFI_MEMORY_NV ? "NV" : "", > attr & EFI_MEMORY_XP ? "XP" : "", > attr & EFI_MEMORY_RP ? "RP" : "", > diff --git a/include/linux/efi.h b/include/linux/efi.h > index 6ebc2098cfe1..91368f5ce114 100644 > --- a/include/linux/efi.h > +++ b/include/linux/efi.h > @@ -112,6 +112,7 @@ typedef struct { > #define EFI_MEMORY_MORE_RELIABLE \ > ((u64)0x0000000000010000ULL) /* higher > reliability */ > #define EFI_MEMORY_RO ((u64)0x0000000000020000ULL) /* read-only > */ > +#define EFI_MEMORY_SP ((u64)0x0000000000040000ULL) /* special > purpose */ > #define EFI_MEMORY_RUNTIME ((u64)0x8000000000000000ULL) /* range > requires runtime mapping */ > #define EFI_MEMORY_DESCRIPTOR_VERSION 1 > >
