On 01/20/17 17:42, Ard Biesheuvel wrote: > On 20 January 2017 at 16:38, Laszlo Ersek <[email protected]> wrote: >> On 01/20/17 17:05, Ard Biesheuvel wrote: >>> After a recent change to the AArch64 page table code, the root table >>> of the page tables is allocated using AllocatePool() rather than >>> AllocatePages() if its size is much smaller than a page. E.g., when >>> using 40 bits of translation, the root table only takes up 16 bytes >>> >>> However, what I have noticed is that pool allocations made during PEI >>> are listed as available memory in the EFI memory map (using memmap in >>> the UEFI Shell). Is this expected? Is it part of the contract that >>> AllocatePool() allocations are lost when entering DXE? >> >> Pool allocations in PEI are satisfied with HOBs (and therefore the pool >> allocation sizes are limited to ~64KB). >> >> In addition, soon after permanent PEI RAM is installed, objects from the >> temporary SEC/PEI heap are moved there (this is called "temporary RAM >> migration"). This includes the migration of the full HOB list, including >> those that were used to satisfy pool allocations prior to RAM migration. >> > > So how is this supposed to work for code that holds a pointer to such > a pool allocation?
It's not. Against such HOBs, don't hold a pointer, hold a grudge. :) > >> If you want to allocate memory in PEI that is to survive in-place into >> DXE and later, I can think of two ways: >> >> - Call AllocatePages. This will only work after permanent PEI RAM has >> been installed (so you might want to make the PEIM performing the call >> dependent on gEfiPeiMemoryDiscoveredPpiGuid, with a DEPEX). The >> allocation will be carved out of the permanent PEI RAM. >> > > The same code calls AllocatePages for the subsequent translation > levels, i.e., when using 40 bits of translation, there are 4 levels, > where all but the top level are full pages. So I could simply replace > AllocatePool with AllocaPages in this case, Yes, I think so. > which would effectively > revert my 'improvement' to this code to use a pool allocation for the > root level. > >> - Allocate a region (a whole multiple of pages) outside of the permanent >> PEI RAM, but in a spot that will later on be backed by system memory >> (due to a system memory resource descriptor HOB produced in PEI, or due >> to a GCD memory space addition during DXE). The way to perform this kind >> of allocation is simply to produce a memory allocation HOB, covering the >> range in question. This works even before the installation of permanent >> PEI RAM. >> >> ... I hope I remembered most of this stuff right. >> > > Thanks for the lesson :-) > You certainly got what you paid for! ;) _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
