On 05/16/19 10:00, Ard Biesheuvel wrote: > On Sat, 4 May 2019 at 02:07, Laszlo Ersek <ler...@redhat.com> wrote: >> >> Commit 7b8fe63561b4 ("OvmfPkg: PlatformPei: enable PCIEXBAR (aka MMCONFIG >> / ECAM) on Q35", 2016-03-10) claimed that, >> >> On Q35 machine types that QEMU intends to support in the long term, QEMU >> never lets the RAM below 4 GB exceed 2 GB. >> >> Alas, this statement came from a misunderstanding that occurred while we >> worked out the interface contract. In fact QEMU does allow the 32-bit RAM >> extend up to 0xB000_0000 (exclusive), in case the RAM size falls in the >> range (0x8000_0000, 0xB000_0000) (i.e., the RAM size is greater than >> 2048MB and smaller than 2816MB). >> >> In turn, such a RAM size (justifiedly) triggers >> >> ASSERT (TopOfLowRam <= PciExBarBase); >> >> in MemMapInitialization(), because we placed the 256MB PCIEXBAR at >> 0x8000_0000 (2GB) exactly, relying on the interface contract. (And, the >> 32-bit PCI hole would follow the PCIEXBAR, covering the [0x9000_0000, >> 0xFC00_0000) range.) >> >> In order to fix this, reorder the 32-bit PCI hole against the PCIEXBAR, as >> follows: >> >> - start the 32-bit PCI hole where it starts on i440fx as well, that is, at >> 2GB or TopOfLowRam, whichever is higher; >> >> - unlike on i440fx, where the 32-bit PCI hole extends up to 0xFC00_0000, >> stop it at 0xE000_0000 on q35, >> >> - place the PCIEXBAR at 0xE000_0000. >> >> (We cannot place the PCIEXBAR at 0xF000_0000 because the 256MB MMIO area >> that starts there is not entirely free.) >> >> Before this patch, the 32-bit PCI hole used to only *end* at the same spot >> (namely, 0xFC00_0000) between i440fx and q35; now it will only *start* at >> the same spot (namely, 2GB or TopOfLowRam, whichever is higher) between >> both boards. >> >> On q35, the maximal hole shrinks from >> >> 0xFC00_0000 - 0x9000_0000 = 0x6C00_0000 == 1728 MB >> >> to >> >> 0xE000_0000 - 0x8000_0000 == 1536 MB. >> >> We lose 192 MB of the aperture; however, the aperture is now aligned at >> 1GB, rather than 256 MB, and so it could fit a 1GB BAR even. >> >> Regarding the minimal hole (triggered by RAM size 2815MB), its size is >> >> 0xE000_0000 - 0xAFF0_0000 = 769 MB >> >> which is not great, but probably better than a failed ASSERT. >> >> Cc: Ard Biesheuvel <ard.biesheu...@linaro.org> >> Cc: Gerd Hoffmann <kra...@redhat.com> >> Cc: Jordan Justen <jordan.l.jus...@intel.com> >> Ref: https://bugzilla.redhat.com/show_bug.cgi?id=1666941 >> Ref: https://bugzilla.redhat.com/show_bug.cgi?id=1701710 >> Contributed-under: TianoCore Contribution Agreement 1.1 >> Signed-off-by: Laszlo Ersek <ler...@redhat.com> > > I take it the 32-bit PCI 'hole' is in fact the 32-bit MMIO BAR window?
Yes, that's correct. We also call it "32-bit PCI MMIO aperture", sometimes. The interval that PciHostBridgeLib passes to PciHostBridgeDxe, to allocate BARs out of, when PciBusDxe asks. > That could do with a clarification. I guess it may be an x86-ism to > consider any physical memory region not used by RAM to be a hole, but > it is not terribly helpful. The "PCI hole" expressions is a QEMU-ism; it is frequently used in connection with the i440fx and q35 (x86) machine types, and not much elsewhere: $ git grep -c pci_hole hw/i386/acpi-build.c:10 hw/i386/pc.c:1 hw/pci-host/grackle.c:3 hw/pci-host/piix.c:23 hw/pci-host/q35.c:24 hw/pci-host/uninorth.c:4 include/hw/i386/pc.h:1 include/hw/pci-host/q35.h:3 include/hw/pci-host/uninorth.h:1 > In any case, > > Reviewed-by: Ard Biesheuvel <ard.biesheu...@linaro.org> Thank you! Laszlo > >> --- >> OvmfPkg/OvmfPkgIa32.dsc | 5 +---- >> OvmfPkg/OvmfPkgIa32X64.dsc | 5 +---- >> OvmfPkg/OvmfPkgX64.dsc | 5 +---- >> OvmfPkg/PlatformPei/Platform.c | 9 ++++----- >> 4 files changed, 7 insertions(+), 17 deletions(-) >> >> diff --git a/OvmfPkg/OvmfPkgIa32.dsc b/OvmfPkg/OvmfPkgIa32.dsc >> index 36a0f87258dd..bb55b6fa58e1 100644 >> --- a/OvmfPkg/OvmfPkgIa32.dsc >> +++ b/OvmfPkg/OvmfPkgIa32.dsc >> @@ -491,10 +491,7 @@ [PcdsFixedAtBuild] >> # This PCD is used to set the base address of the PCI express hierarchy. >> It >> # is only consulted when OVMF runs on Q35. In that case it is programmed >> into >> # the PCIEXBAR register. >> - # >> - # On Q35 machine types that QEMU intends to support in the long term, QEMU >> - # never lets the RAM below 4 GB exceed 2 GB. >> - gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress|0x80000000 >> + gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress|0xE0000000 >> >> !ifdef $(SOURCE_DEBUG_ENABLE) >> gEfiSourceLevelDebugPkgTokenSpaceGuid.PcdDebugLoadImageMethod|0x2 >> diff --git a/OvmfPkg/OvmfPkgIa32X64.dsc b/OvmfPkg/OvmfPkgIa32X64.dsc >> index 9b341e17d7ff..06c394a6fb1f 100644 >> --- a/OvmfPkg/OvmfPkgIa32X64.dsc >> +++ b/OvmfPkg/OvmfPkgIa32X64.dsc >> @@ -496,10 +496,7 @@ [PcdsFixedAtBuild] >> # This PCD is used to set the base address of the PCI express hierarchy. >> It >> # is only consulted when OVMF runs on Q35. In that case it is programmed >> into >> # the PCIEXBAR register. >> - # >> - # On Q35 machine types that QEMU intends to support in the long term, QEMU >> - # never lets the RAM below 4 GB exceed 2 GB. >> - gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress|0x80000000 >> + gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress|0xE0000000 >> >> !ifdef $(SOURCE_DEBUG_ENABLE) >> gEfiSourceLevelDebugPkgTokenSpaceGuid.PcdDebugLoadImageMethod|0x2 >> diff --git a/OvmfPkg/OvmfPkgX64.dsc b/OvmfPkg/OvmfPkgX64.dsc >> index a0f87f74dab9..5e0eb043fab9 100644 >> --- a/OvmfPkg/OvmfPkgX64.dsc >> +++ b/OvmfPkg/OvmfPkgX64.dsc >> @@ -496,10 +496,7 @@ [PcdsFixedAtBuild] >> # This PCD is used to set the base address of the PCI express hierarchy. >> It >> # is only consulted when OVMF runs on Q35. In that case it is programmed >> into >> # the PCIEXBAR register. >> - # >> - # On Q35 machine types that QEMU intends to support in the long term, QEMU >> - # never lets the RAM below 4 GB exceed 2 GB. >> - gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress|0x80000000 >> + gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress|0xE0000000 >> >> !ifdef $(SOURCE_DEBUG_ENABLE) >> gEfiSourceLevelDebugPkgTokenSpaceGuid.PcdDebugLoadImageMethod|0x2 >> diff --git a/OvmfPkg/PlatformPei/Platform.c b/OvmfPkg/PlatformPei/Platform.c >> index 9c013613a1a0..fd8eccaf3e50 100644 >> --- a/OvmfPkg/PlatformPei/Platform.c >> +++ b/OvmfPkg/PlatformPei/Platform.c >> @@ -184,14 +184,13 @@ MemMapInitialization ( >> PciBase = (TopOfLowRam < BASE_2GB) ? BASE_2GB : TopOfLowRam; >> if (mHostBridgeDevId == INTEL_Q35_MCH_DEVICE_ID) { >> // >> - // The MMCONFIG area is expected to fall between the top of low RAM >> and >> - // the base of the 32-bit PCI host aperture. >> + // The 32-bit PCI host aperture is expected to fall between the top of >> + // low RAM and the base of the MMCONFIG area. >> // >> PciExBarBase = FixedPcdGet64 (PcdPciExpressBaseAddress); >> - ASSERT (TopOfLowRam <= PciExBarBase); >> + ASSERT (PciBase < PciExBarBase); >> ASSERT (PciExBarBase <= MAX_UINT32 - SIZE_256MB); >> - PciBase = (UINT32)(PciExBarBase + SIZE_256MB); >> - PciSize = 0xFC000000 - PciBase; >> + PciSize = (UINT32)(PciExBarBase - PciBase); >> } else { >> PciSize = 0xFC000000 - PciBase; >> } >> -- >> 2.19.1.3.g30247aa5d201 >> >> >> >> ------------ >> Groups.io Links: You receive all messages sent to this group. >> >> View/Reply Online (#39968): https://edk2.groups.io/g/devel/message/39968 >> Mute This Topic: https://groups.io/mt/31489698/1761188 >> Group Owner: devel+ow...@edk2.groups.io >> Unsubscribe: https://edk2.groups.io/g/devel/unsub >> [ard.biesheu...@linaro.org] >> ------------ >> -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. 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