On Mon, Sep 16, 2013 at 01:50:46PM +0200, Laszlo Ersek wrote: > On 09/16/13 12:59, Matt Fleming wrote: > > On Fri, 13 Sep, at 02:38:12PM, jerry.hoemann@xxxxxx wrote: > >> Matt, > >> > >> We have hit an issue on our new platform in development related to the > >> call of efi_reserve_boot_services() from setup_arch(). > >> > >> The reservation can interfere with allocation of the crash kernel. > > > > Jerry, thanks for bringing this up. > > > >> In pre 3.9(?) kernels, the crash kernel is required to be allocated from > >> physically contiguous memory below 896 MB. > >> > >> Our new platforms are large in both the amount of memory and the amount > >> of IO. This requires large crash kernels for kdump to work. This is even > >> after the work done for makedumpfile v 1.5 to allow it to work with a > >> smaller foot print. > >> > >> > >> One of the problems is that drivers will allocate memory as boot code and/or > >> data in the region < 896 that effectively fragments this memory. > >> With the reservation, we can't reuse the memory when needed for the > >> crash kernels. If we remove the reservation and allow the kernel > >> to reuse the memory, we the reservation of the crash kernel succeeds. > >> > >> This is definitely a problem for distros that are pre 3.9. Probably less > >> so for top of tree, but i haven't been focused there. > >> > >> So we are definitely interested in finding a mechanism to not > >> do this reservation on platforms that don't have the issues described > >> earlier in this thread. > > > > OK, in an ideal world we'd move the crash kernel reservation after > > efi_free_boot_services(), because at that point the boot regions are > > available again. But it seems that we reserve the boot regions really > > early during startup and release them relatively late. The reason is > > that the Boot Graphics Resource Table (BGRT) data, if present, is > > located in the Boot Services Data regions but we can't extract the > > address of the region from the ACPI tables until we've setup the ACPI > > subsystem, which happens quite late. > > Why is BGRT allocated as Boot Services Data? > > In file > "MdeModulePkg/Universal/Acpi/BootGraphicsResourceTableDxe/BootGraphicsResourceTableDxe.c": > > InstallBootGraphicsResourceTable() > BgrtAllocateBsDataMemoryBelow4G() > gBS->AllocatePages(... EfiBootServicesData ...) > > From Table 25. Memory Type Usage before ExitBootServices(): > > EfiBootServicesData -- The data portions of a loaded Boot Services > Driver, and the default data allocation type > used by a Boot Services Driver to allocate > pool memory. > > EfiACPIReclaimMemory -- Memory that holds the ACPI tables. > > From Table 26. Memory Type Usage after ExitBootServices(): > > EfiBootServicesData -- Memory available for general use. > > EfiACPIReclaimMemory -- This memory is to be preserved by the loader > and OS until ACPI is enabled. Once ACPI is > enabled, the memory in this range is available > for general use. > > I thought that anything referenced by a pointer in any ACPI table was > EfiACPIReclaimMemory or stricter. Specifically, the RSDT or XSDT points > to BGRT, so BGRT is EfiACPIReclaimMemory. BGRT points to the image data > (with its Image Address field), hence the image data should be > EfiACPIReclaimMemory too. > > Otherwise, the pointer (BGRT.ImageAddress) can outlive the pointed-to > storage (the image data). > > The image data sounds to me like textbook example for > EfiACPIReclaimMemory. This way the kernel could free Boot Services Data > early, perform the crash kernel reservation right after, and safely > access BGRT whenever the ACPI subsystem is brought up later. > > > The edk2 commit that flipped the memory type underneath the image data > from EfiReservedMemoryType to EfiBootServicesData is: > > https://github.com/tianocore/edk2/commit/4c58575e > > I think this commit is wrong. It's fine for OSPM to release the image > data at some point, but not right after ExitBootServices(), because > referencing pointers in ACPI tables survive strictly longer. > > ... Actually, the commit does follow the ACPI spec 5.0: > > 5.2.22.4 Image Address > > The Image Address contains the location in memory where an > in-memory copy of the boot image can be found. The image should be > stored in EfiBootServicesData, allowing the system to reclaim > the memory when the image is no longer needed. > > The ACPI spec 5.0 should recommend EfiACPIReclaimMemory here IMO. (I > take the current wording ("should be stored") as a recommendation only.) I agree that UEFI *should* store the BGRT in EfiACPIReclaimMemory, but in practice the UEFI firmware I've seen with a BGRT does follow that recommendation and store it in EfiBootServicesData. So, even if the recommendation in the spec changed, the kernel would still have to accomodate both possibilities. - Josh Triplett -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
