Hi Laszlo, On 5/16/19 2:18 PM, Laszlo Ersek wrote: > 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.
Maybe you can amend that comment, ... > >> 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 ... and this one in the commit description. Regardless: Reviewed-by: Philippe Mathieu-Daude <phi...@redhat.com> > 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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