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? > 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, 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 :-) _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
