mirror of https://github.com/acidanthera/audk.git
39b9a5ffe6
Assume that we boot OVMF in a QEMU guest with 1025 MB of RAM. The following assertion will fire: > ASSERT_EFI_ERROR (Status = Out of Resources) > ASSERT OvmfPkg/PlatformPei/MemDetect.c(696): !EFI_ERROR (Status) That's because the range [1025 MB, 4 GB) that we try to mark as uncacheable with MTRRs has size 3071 MB: 0x1_0000_0000 -0x0_4010_0000 -------------- 0x0_BFF0_0000 The integer that stands for the uncacheable area size has 11 (eleven) bits set to 1. As a result, covering this size requires 11 variable MTRRs (each MTRR must cover a naturally aligned, power-of-two sized area). But, if we need more variable MTRRs than the CPU can muster (such as 8), then MtrrSetMemoryAttribute() fails, and we refuse to continue booting (which is justified, in itself). Unfortunately, this is not difficult to trigger, and the error message is well-hidden from end-users, in the OVMF debug log. The following mitigation is inspired by SeaBIOS: Truncate the uncacheable area size to a power-of-two, while keeping the end fixed at 4 GB. Such an interval can be covered by just one variable MTRR. This may leave such an MMIO gap, between the end of low-RAM and the start of the uncacheable area, that is marked as WB (through the MTRR default). Raise the base of the 32-bit PCI MMIO aperture accordingly -- the gap will not be used for anything. On Q35, the minimal 32-bit PCI MMIO aperture (triggered by RAM size 2815 MB) shrinks from 0xE000_0000 - 0xAFF0_0000 = 769 MB to 0xE000_0000 - 0xC000_0000 = 512 MB On i440fx, the minimal 32-bit PCI MMIO aperture (triggered by RAM size 3583 MB) shrinks from 0xFC00_0000 - 0xDFF0_0000 = 449 MB to 0xFC00_0000 - 0xE000_0000 = 448 MB Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org> Cc: Gerd Hoffmann <kraxel@redhat.com> Cc: Jordan Justen <jordan.l.justen@intel.com> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1814 Ref: https://bugzilla.redhat.com/show_bug.cgi?id=1666941 Ref: https://bugzilla.redhat.com/show_bug.cgi?id=1701710 Signed-off-by: Laszlo Ersek <lersek@redhat.com> Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> |
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| .. | ||
| AmdSev.c | ||
| ClearCache.c | ||
| Cmos.c | ||
| Cmos.h | ||
| FeatureControl.c | ||
| Fv.c | ||
| MemDetect.c | ||
| Platform.c | ||
| Platform.h | ||
| PlatformPei.inf | ||
| Xen.c | ||
| Xen.h | ||