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[[email protected]: Re: aarch64 efi boot failures with qemu 6.0+]

[email protected]: Re: aarch64 efi boot failures with qemu 6.0+ Bjorn Helgaas 1 participant 1 message Jul 26, 2021

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Bjorn Helgaas

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Just FYI.

Guenter tripped over a problem with an I/O BAR set to zero. I think your arches allow that (at least they "#define PCIBIOS_MIN_IO 0"), and some drivers don't handle such BARs. More details below.

Note that I didn't actually cc you on the thread, mostly because I forgot but partly to avoid exploding the cc list with people who probably don't care. If you want to respond directly to the thread, you can use this:

https://lore.kernel.org/qemu-devel/[email protected]/

----- Forwarded message from Bjorn Helgaas <[email protected]> -----

Date: Mon, 26 Jul 2021 16:16:29 -0500
From: Bjorn Helgaas <[email protected]>
To: Ard Biesheuvel <[email protected]>
Cc: Philippe Mathieu-Daudé <[email protected]>, Bjorn Helgaas
<[email protected]>, Jiahui Cen <[email protected]>, "Michael S. Tsirkin" <[email protected]>, Ard Biesheuvel <[email protected]>, [email protected], Igor Mammedov <[email protected]>, Guenter Roeck <[email protected]>
Subject: Re: aarch64 efi boot failures with qemu 6.0+
Message-ID: <20210726211628.GA640636@bjorn-Precision-5520>

Quoted 39 lines · Ard Biesheuvel

(cc Bjorn)

Quoted 12 lines · Philippe Mathieu-Daudé
Quoted 11 lines · Guenter Roeck
Quoted 10 lines · Michael S. Tsirkin
Quoted 9 lines · Guenter Roeck

Hi all,

starting with qemu v6.0, some of my aarch64 efi boot tests no longer work. Analysis shows that PCI devices with IO ports do not instantiate in qemu v6.0 (or v6.1-rc0) when booting through efi. The problem affects (at least) ne2k_pci, tulip, dc390, and am53c974. The problem only affects
aarch64, not x86/x86_64.

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I bisected the problem to commit 0cf8882fd0 ("acpi/gpex: Inform os to keep firmware resource map"). Since this commit, PCI device BAR allocation has changed. Taking tulip as example, the kernel reports the following PCI bar assignments when running qemu v5.2.

[    3.921801] pci 0000:00:01.0: [1011:0019] type 00 class 0x020000
[    3.922207] pci 0000:00:01.0: reg 0x10: [io  0x0000-0x007f]
[    3.922505] pci 0000:00:01.0: reg 0x14: [mem 0x10000000-0x1000007f]

IIUC, these lines are read back from the BARs

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[    3.927111] pci 0000:00:01.0: BAR 0: assigned [io  0x1000-0x107f]
[    3.927455] pci 0000:00:01.0: BAR 1: assigned [mem

0x10000000-0x1000007f]

... and this is the assignment created by the kernel.

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With qemu v6.0, the assignment is reported as follows.

[    3.922887] pci 0000:00:01.0: [1011:0019] type 00 class 0x020000
[    3.923278] pci 0000:00:01.0: reg 0x10: [io  0x0000-0x007f]
[    3.923451] pci 0000:00:01.0: reg 0x14: [mem 0x10000000-0x1000007f]
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The problem here is that Linux, for legacy reasons, does not support I/O ports <= 0x1000 on PCI, so the I/O assignment created by EFI is rejected.

This might make sense on x86, where legacy I/O ports may exist, but on other architectures, this makes no sense.

I guess this is the "#define PCIBIOS_MIN_IO 0x1000" in arm64/include/asm/pci.h. From a PCI point of view, I'm not opposed to changing that to 0, as it is on csky, riscv, sh, sparc, um. But it's really an arch question, so the arm64 folks would have to weigh in.

But I don't think that would fix this. PCIBIOS_MIN_IO is mainly used when we assign or reassign resources to a BAR, and if firmware tells us to preserve the assignments done by firmware, Linux shouldn't be doing any assignment or reassignment.

Linux received 00:01.0 BAR 0 as [io 0x0000-0x007f], and Guenter didn't report any reassignment, so I assume Linux saw the DSM_PCI_PRESERVE_BOOT_CONFIG [1] and didn't change anything.

Could this be due to drivers assuming that an I/O BAR of 0 is invalid? I see that at least ne2k_pci_init_one() [2] seems to assume that. And tulip_init_one() [3] and pci_esp_probe_one() (am53c974.c, [4]) use pci_iomap() [5], which fails if the resource starts at 0.

So pci_iomap() is probably already broken on the arches above that allow I/O BARs to be zero. Maybe pci_iomap() should only fail on "!start" for *memory* BARs, e.g.,

lib/pci_iomap.c +3 -1
index 2d3eb1cb73b8..77455e702a3e 100644
@@ -34,7 +34,9 @@ void __iomem *pci_iomap_range(struct pci_dev *dev,
 	resource_size_t len = pci_resource_len(dev, bar);
 	unsigned long flags = pci_resource_flags(dev, bar);
 
-	if (len <= offset || !start)
+	if (flags & IORESOURCE_MEM && !start)
+		return NULL;
+	if (len <= offset)
 		return NULL;
 	len -= offset;
 	start += offset;

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/acpi/pci_root.c?id=v5.13#n915
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/ethernet/8390/ne2k-pci.c?id=v5.13#n247
[3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/ethernet/dec/tulip/tulip_core.c?id=v5.13#n1418
[4] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/scsi/am53c974.c?id=v5.13#n431
[5] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/pci_iomap.c?id=v5.13#n37

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and the controller does not instantiate. The problem disapears after reverting commit 0cf8882fd0.

Attached is a summary of test runs with various devices and qemu v5.2 as well as qemu v6.0, and the command line I use for efi boots.

Did commit 0cf8882fd0 introduce a bug, do I now need need some different command line to instantiate PCI devices with io ports, or are such devices
simply no longer supported if the system is booted with efi support ?

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Thanks,
Guenter

So that commit basically just says don't ignore what efi did.

The issue's thus likely efi.

I don't see the problem with efi boots on x86 and x86_64. Any idea why that might be the case ?

Thanks,
Guenter

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Cc the maintainer. Philippe can you comment pls?

I'll have a look. Cc'ing Ard for EDK2/Aarch64.

So a potential workaround would be to use a different I/O resource window for ArmVirtPkg, that starts at 0x1000. But I would prefer to fix Linux instead.

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---
Command line (tulip network interface):

CMDLINE="root=/dev/vda console=ttyAMA0"
ROOTFS="rootfs.ext2"

qemu-system-aarch64 -M virt -kernel arch/arm64/boot/Image -no-reboot \
         -m 512 -cpu cortex-a57 -no-reboot \
         -device tulip,netdev=net0 -netdev user,id=net0 \
         -bios QEMU_EFI-aarch64.fd \
         -snapshot \
         -device virtio-blk-device,drive=d0 \
         -drive file=${ROOTFS},if=none,id=d0,format=raw \
         -nographic -serial stdio -monitor none \
         --append "${CMDLINE}"

---
Boot tests with various devices known to work in qemu v5.2.

v5.2 v6.0 v6.0
efi non-efi efi
e1000 pass pass pass

e1000-82544gc    pass    pass    pass
e1000-82545em    pass    pass    pass
e1000e        pass    pass    pass
i82550        pass    pass    pass
i82557a        pass    pass    pass
i82557b        pass    pass    pass
i82557c        pass    pass    pass
i82558a        pass    pass    pass
i82559b        pass    pass    pass
i82559c        pass    pass    pass
i82559er    pass    pass    pass
i82562        pass    pass    pass
i82801        pass    pass    pass

ne2k_pci pass pass fail <--
pcnet pass pass pass
rtl8139 pass pass pass
tulip pass pass fail <--
usb-net pass pass pass
virtio-net-device
pass pass pass
virtio-net-pci pass pass pass
virtio-net-pci-non-transitional
pass pass pass

usb-xhci    pass    pass    pass
usb-ehci    pass    pass    pass
usb-ohci    pass    pass    pass

usb-uas-xhci pass pass pass
virtio pass pass pass
virtio-blk-pci pass pass pass
virtio-blk-device
pass pass pass
nvme pass pass pass

sdhci        pass    pass    pass
dc390        pass    pass    fail    <--

am53c974 pass pass fail <--
lsi53c895ai pass pass pass
mptsas1068 pass pass pass
lsi53c810 pass pass pass
megasas pass pass pass
megasas-gen2 pass pass pass
virtio-scsi-device
pass pass pass
virtio-scsi-pci pass pass pass

----- End forwarded message -----