Re: [edk2] Corrupted EFI region

Josh Triplett
2013-09-16T15:57:51Z

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-VXdhtT5mjnY@public.gmane.org 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