Revert "MdePkg/ProcessorBind.h AARCH64: limit MAX_ADDRESS to 48 bits"
authorArd Biesheuvel <ard.biesheuvel@linaro.org>
Thu, 6 Dec 2018 21:10:36 +0000 (22:10 +0100)
committerArd Biesheuvel <ard.biesheuvel@linaro.org>
Fri, 7 Dec 2018 11:24:19 +0000 (12:24 +0100)
commita5274cdc87d952a4609b0baef92df3a4b6a36059
treeab88018a9fd8c1ee55fcc321aeb26c1a5e3042c9
parent9601046bf4594be981b6ee9f75f81f0bc0e2cf54
Revert "MdePkg/ProcessorBind.h AARCH64: limit MAX_ADDRESS to 48 bits"

This reverts commit 82379bf6603274e81604d5a6f6bb14bdde616286.

On AArch64, we can only use 48 address bits while running in UEFI,
while the GCD and UEFI memory maps may describe up to 52 bits of
physical address space. For this reason, MAX_ADDRESS was reduced
to 48 bits, to ensure that the firmware does not inadvertently
attempt to allocate memory that we cannot access.

However, MAX_ADDRESS is used in runtime drivers as well, and
runtime drivers may deal with kernel virtual addresses, which have
bits [63:48] set. In fact, the OS may be running with 64 KB pages
and pass addresses into the runtime services that use up to 52
bits of address space, either with the top bits set or cleared,
even if the physical address space does not extend beyond 48 bits.

In summary, changing MAX_ADDRESS is a mistake, and needs to be
reverted.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
MdePkg/Include/AArch64/ProcessorBind.h