Re: [PATCH v2 00/28] x86: Improve operation under QEMU

[Simon Glass <sjg@chromium.org>]

Hi Paolo,

On Sun, 16 Feb 2025 at 14:14, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 2/16/25 21:43, Simon Glass wrote:
> > U-Boot can start and boot an OS in both qemu-x86 and qemu-x86_64 but it
> > is not perfect.
> >
> > With both builds, executing the VESA ROM causes an intermittent hang, at
> > least on some AMD CPUs.
> >
> > With qemu-x86_64 kvm cannot be used since the move to long mode (64-bit)
> > is done in a way that works on real hardware but not with QEMU. This
> > means that performance is 4-5x slower than it could be, at least on my
> > CPU.
>
> Do you have a reproducer for this?  It shouldn't happen... also, do you
> know if this is broken for both Intel and AMD CPUs?

You can see this if you build the right commit (e52e307c7ca) from my
tree[1], i.e. after U-Boot changes to Bochs and before it changes the
64-bit entry mechanism:

04:57 $ pe
e52e307c7ca (HEAD) x86: qemu: Switch to bochs display
83f8b00df47 x86: Expand x86_64 early memory
71a6c3eb3d8 Revert "efi_memory: do not add U-Boot memory to the memory map"
d9d87e11e97 test: Make net tests depend on CONFIG_CMD_NET
3c67e62b109 test/py: Show info about module-loading
7059d976d22 test/py: Drop assigning ubman to cons
e361abfc638 test/py: Drop importing utils as util
460ecb6e5cd test/py: Drop u_boot_ prefix on test files
cc5600e734c test/py: Shorten u_boot_console
777c7a0c20e test: Update documentation
✔ ~/u [:e52e307c7ca|…6⚑ 1160]
04:57 $ ./tools/buildman/buildman --bo qemu-x86_64 -o /tmp/b/qemu-x86_64/ -w
Building current source for 1 boards (1 thread, 32 jobs per thread)
    1    0    0 /1              qemu-x86_64
Completed: 1 total built, 1 newly), duration 0:00:02, rate 0.50
✔ ~/u [:e52e307c7ca|…6⚑ 1160]
04:57 $ qemu-system-x86_64 -bios /tmp/b/qemu-x86_64/u-boot.rom
-enable-kvm    -nographic
Running qemu-system-x86_64  -display none -serial mon:stdio

U-Boot SPL 2025.01-rc3-00635-ge52e307c7ca8 (Feb 17 2025 - 04:57:59 -0700)
Trying to boot from SPI
Jumping to 64-bit U-Boot: Note many features are missing
(hangs here)
QEMU: Terminated

I am running this on an AMD system. But I just tried it on an Intel
laptop and it has the same issue.
>
> Thanks,
>
> Paolo
>
Regards,
Simon

> > We can work around the first problem by using Bochs, which is anyway a
> > better choice than VESA for QEMU. The second can be addressed by using
> > the same descriptor across the jump to long mode.
> >
> > With an MTRR fix this allows booting into Ubuntu on qemu-x86_64
> >
> > Changes in v2:
> > - Redo commit message
> > - Add new patch to rename the _D dirty flag
> > - Add new patch to support CPU functions in long mode
> > - Add new patch to tidy up address size in MTRR calculations
> > - Add new patch with a 64-bit version of is_power_of_2()
> > - Add new patch to set an MTRR for the RAM in QEMU
> > - Add new patch with a helper to send characters
> > - Add new patch to allow tests to be filtered by role
> > - Add more patches to support booting with kvm
> > - Add new patch with a test for booting Ubuntu 24.04
> >
> > Simon Glass (28):
> >    x86: Expand x86_64 early memory
> >    x86: qemu: Switch to bochs display
> >    x86: qemu: Enable dhrystone
> >    x86: qemu: Avoid accessing BSS too early
> >    x86: Drop mpspec from the SPL build
> >    x86: Add some log categories
> >    x86: Drop use of CONFIG_REALMODE_DEBUG
> >    x86: Avoid clearing the VESA display
> >    x86: Add 64-bit entries to the GDT
> >    x86: Use defines for the cache flags
> >    x86: spl: Drop duplicate CPU init
> >    x86: Drop the message about features missing in 64-bit
> >    x86: Include stdbool.h in interrupt header
> >    x86: Tidy up the GDT size in start/16.S
> >    x86: Disable paging before changing to long mode
> >    x86: Use the same GDT when jumping to long mode
> >    x86: Use a simple jump into long mode
> >    x86: Rename the _D dirty flag
> >    x86: Support CPU functions in long mode
> >    x86: Tidy up address size in MTRR calculations
> >    Add a 64-bit version of is_power_of_2()
> >    x86: Support MTRRs of 4GB on 32-bit machines
> >    x86: emulation: Set an MTRR for the RAM
> >    scripts: Expand a few options
> >    test/py: Add a helper to send characters
> >    test/py: Allow tests to be filtered by role
> >    RFC: test/py: Deal with timeouts
> >    test: Add a test for booting Ubuntu 24.04
> >
> >   .gitlab-ci.yml                   |  5 +++
> >   arch/x86/cpu/cpu.c               | 24 +++++++++++++++
> >   arch/x86/cpu/i386/call64.S       | 35 +++++++++------------
> >   arch/x86/cpu/i386/cpu.c          | 41 +++++++++---------------
> >   arch/x86/cpu/mtrr.c              | 12 +++++---
> >   arch/x86/cpu/qemu/dram.c         | 15 +++++++++
> >   arch/x86/cpu/qemu/qemu.c         | 20 ++++++++----
> >   arch/x86/cpu/start.S             |  4 ++-
> >   arch/x86/cpu/start16.S           |  3 +-
> >   arch/x86/cpu/x86_64/cpu.c        |  5 ---
> >   arch/x86/include/asm/cpu.h       | 35 ++++++++++++++++++---
> >   arch/x86/include/asm/interrupt.h |  1 +
> >   arch/x86/include/asm/processor.h |  5 ++-
> >   arch/x86/lib/Makefile            |  2 ++
> >   arch/x86/lib/bios.c              | 27 +++++++++-------
> >   arch/x86/lib/bios_interrupts.c   |  8 ++---
> >   arch/x86/lib/i8259.c             |  2 ++
> >   arch/x86/lib/spl.c               |  4 +--
> >   configs/qemu-x86_64_defconfig    | 10 +++---
> >   configs/qemu-x86_defconfig       |  6 ++--
> >   include/linux/log2.h             |  6 ++++
> >   scripts/build-qemu.sh            |  4 +--
> >   test/py/conftest.py              | 22 +++++++++++++
> >   test/py/console_base.py          | 33 ++++++++++++--------
> >   test/py/pytest.ini               |  1 +
> >   test/py/tests/test_distro.py     | 53 ++++++++++++++++++++++++++++++++
> >   test/py/tests/test_sleep.py      |  1 +
> >   27 files changed, 273 insertions(+), 111 deletions(-)
> >   create mode 100644 test/py/tests/test_distro.py
> >
>

[1] https://ci.u-boot.org/u-boot/u-boot/-/commits/qemu?ref_type=heads