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ArmPkg/CpuDxe ARM: avoid splitting page table sections unnecessarily 

Currently, any range passed to CpuArchProtocol::SetMemoryAttributes is
fully broken down into page mappings if the start or the size of the
region happens to be misaliged relative to the section size of 1 MB.

This is going to result in memory being wasted on second level page tables
when we enable strict memory permissions, given that we remap the entire
RAM space non-executable (modulo the code bits) when the CpuArchProtocol
is installed.

So refactor the code to iterate over the range in a way that ensures
that all naturally aligned section sized subregions are not broken up.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
This commit is contained in:
Ard Biesheuvel 2017-03-02 10:36:13 +00:00
parent 5b0ce08a3e
commit df809efe13
1 changed files with 43 additions and 8 deletions
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51
ArmPkg/Drivers/CpuDxe/Arm/Mmu.c
View File

@ -679,6 +679,11 @@ SetMemoryAttributes (
)
{
EFI_STATUS Status;
UINT64 ChunkLength;
if (Length == 0) {
return EFI_SUCCESS;
}
//
// Ignore invocations that only modify permission bits
@ -687,14 +692,44 @@ SetMemoryAttributes (
return EFI_SUCCESS;
}
if(((BaseAddress & 0xFFFFF) == 0) && ((Length & 0xFFFFF) == 0)) {
// Is the base and length a multiple of 1 MB?
DEBUG ((EFI_D_PAGE, "SetMemoryAttributes(): MMU section 0x%x length 0x%x to %lx\n", (UINTN)BaseAddress, (UINTN)Length, Attributes));
Status = UpdateSectionEntries (BaseAddress, Length, Attributes, VirtualMask);
} else {
// Base and/or length is not a multiple of 1 MB
DEBUG ((EFI_D_PAGE, "SetMemoryAttributes(): MMU page 0x%x length 0x%x to %lx\n", (UINTN)BaseAddress, (UINTN)Length, Attributes));
Status = UpdatePageEntries (BaseAddress, Length, Attributes, VirtualMask);
while (Length > 0) {
if ((BaseAddress % TT_DESCRIPTOR_SECTION_SIZE == 0) &&
Length >= TT_DESCRIPTOR_SECTION_SIZE) {
ChunkLength = Length - Length % TT_DESCRIPTOR_SECTION_SIZE;
DEBUG ((DEBUG_PAGE,
"SetMemoryAttributes(): MMU section 0x%lx length 0x%lx to %lx\n",
BaseAddress, ChunkLength, Attributes));
Status = UpdateSectionEntries (BaseAddress, ChunkLength, Attributes,
VirtualMask);
} else {
//
// Process page by page until the next section boundary, but only if
// we have more than a section's worth of area to deal with after that.
//
ChunkLength = TT_DESCRIPTOR_SECTION_SIZE -
(BaseAddress % TT_DESCRIPTOR_SECTION_SIZE);
if (ChunkLength + TT_DESCRIPTOR_SECTION_SIZE > Length) {
ChunkLength = Length;
}
DEBUG ((DEBUG_PAGE,
"SetMemoryAttributes(): MMU page 0x%lx length 0x%lx to %lx\n",
BaseAddress, ChunkLength, Attributes));
Status = UpdatePageEntries (BaseAddress, ChunkLength, Attributes,
VirtualMask);
}
if (EFI_ERROR (Status)) {
break;
}
BaseAddress += ChunkLength;
Length -= ChunkLength;
}
// Flush d-cache so descriptors make it back to uncached memory for subsequent table walks