[Qemu-devel] [Bug 796202] [NEW] Doing a 64 bit load from a 32 bit local APIC register is allowed

[Qemu-devel] [Bug 796202] [NEW] Doing a 64 bit load from a 32 bit local APIC register is allowed

[Robert Uhl]

Public bug reported:

Doing

u64 lapic_idregister = (u64) fix_to_virt(FIX_APIC_BASE) + 0x20;

and later in an interrupt handler

movq (lapic_idregister), %rcx
movq (%rcx), %rcx

in a linux kernel module works in qemu 0.13.91 but not on real hardware (it simply reboots).
On real hardware only

movl (%rcx), %ecx

works (also in qemu).

Commandline:
qemu-system-x86_64 \
		-kernel $LINUXDIR/arch/x86_64/boot/bzImage \
		-hda $BUILDROOTDIR/output/images/rootfs.ext2 \
		-append "root=/dev/sda rw rootfstype=ext2 maxcpus=4" \
		-cpu phenom \
		-smp 4 \
		-gdb tcp::1234 \
		-net nic -net user

Guest:
Vanilla Linux Kernel 2.6.37.6 64-bit with buildroot

Mikael Pettersson from the linux kernel mailinglist told me it's an
accepts-invalid bug in qemu.

** Affects: qemu
     Importance: Undecided
         Status: New

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Title:
  Doing a 64 bit load from a 32 bit local APIC register is allowed

Status in QEMU:
  New

Bug description:
  Doing

  u64 lapic_idregister = (u64) fix_to_virt(FIX_APIC_BASE) + 0x20;

  and later in an interrupt handler

  movq (lapic_idregister), %rcx
  movq (%rcx), %rcx

  in a linux kernel module works in qemu 0.13.91 but not on real hardware (it simply reboots).
  On real hardware only

  movl (%rcx), %ecx

  works (also in qemu).

  Commandline:
  qemu-system-x86_64 \
  		-kernel $LINUXDIR/arch/x86_64/boot/bzImage \
  		-hda $BUILDROOTDIR/output/images/rootfs.ext2 \
  		-append "root=/dev/sda rw rootfstype=ext2 maxcpus=4" \
  		-cpu phenom \
  		-smp 4 \
  		-gdb tcp::1234 \
  		-net nic -net user

  Guest:
  Vanilla Linux Kernel 2.6.37.6 64-bit with buildroot

  Mikael Pettersson from the linux kernel mailinglist told me it's an
  accepts-invalid bug in qemu.

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/796202/+subscriptions

Re: [Qemu-devel] [Bug 796202] [NEW] Doing a 64 bit load from a 32 bit local APIC register is allowed

[Blue Swirl]

On Sun, Jun 12, 2011 at 4:03 PM, Robert Uhl <796202@bugs.launchpad.net> wrote:
> Public bug reported:
>
> Doing
>
> u64 lapic_idregister = (u64) fix_to_virt(FIX_APIC_BASE) + 0x20;
>
> and later in an interrupt handler
>
> movq (lapic_idregister), %rcx
> movq (%rcx), %rcx
>
> in a linux kernel module works in qemu 0.13.91 but not on real hardware (it simply reboots).
> On real hardware only
>
> movl (%rcx), %ecx
>
> works (also in qemu).

Thank you for the report. Currently QEMU devices only provide access
methods up to 32 bits, a 64 bit access is emulated with two 32 bit
accesses. So it is not possible to handle a 32 bit access differently
from a 64 bit one for now.

So far this hasn't been considered to be a problem for x86, though it
is clearly not correct for Sparc and Alpha. This report shows that it
is necessary to add 64 bit access methods (or otherwise handle 64 bit
accesses more realistically) since x86 is also affected.

Adding the 64 bit method would be a major refactoring though and there
are other designs possible.

[Qemu-devel] [Bug 796202] Re: Doing a 64 bit load from a 32 bit local APIC register is allowed

[Thomas Huth]

Triaging old bug tickets ... can you somehow still reproduce this
problem with the latest version of QEMU (currently v2.9), or could we
close this ticket nowadays?

** Changed in: qemu
       Status: Confirmed => Incomplete

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You received this bug notification because you are a member of qemu-
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https://bugs.launchpad.net/bugs/796202

Title:
  Doing a 64 bit load from a 32 bit local APIC register is allowed

Status in QEMU:
  Incomplete

Bug description:
  Doing

  u64 lapic_idregister = (u64) fix_to_virt(FIX_APIC_BASE) + 0x20;

  and later in an interrupt handler

  movq (lapic_idregister), %rcx
  movq (%rcx), %rcx

  in a linux kernel module works in qemu 0.13.91 but not on real hardware (it simply reboots).
  On real hardware only

  movl (%rcx), %ecx

  works (also in qemu).

  Commandline:
  qemu-system-x86_64 \
  		-kernel $LINUXDIR/arch/x86_64/boot/bzImage \
  		-hda $BUILDROOTDIR/output/images/rootfs.ext2 \
  		-append "root=/dev/sda rw rootfstype=ext2 maxcpus=4" \
  		-cpu phenom \
  		-smp 4 \
  		-gdb tcp::1234 \
  		-net nic -net user

  Guest:
  Vanilla Linux Kernel 2.6.37.6 64-bit with buildroot

  Mikael Pettersson from the linux kernel mailinglist told me it's an
  accepts-invalid bug in qemu.

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/796202/+subscriptions

[Qemu-devel] [Bug 796202] Re: Doing a 64 bit load from a 32 bit local APIC register is allowed

[Launchpad Bug Tracker]

[Expired for QEMU because there has been no activity for 60 days.]

** Changed in: qemu
       Status: Incomplete => Expired

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https://bugs.launchpad.net/bugs/796202

Title:
  Doing a 64 bit load from a 32 bit local APIC register is allowed

Status in QEMU:
  Expired

Bug description:
  Doing

  u64 lapic_idregister = (u64) fix_to_virt(FIX_APIC_BASE) + 0x20;

  and later in an interrupt handler

  movq (lapic_idregister), %rcx
  movq (%rcx), %rcx

  in a linux kernel module works in qemu 0.13.91 but not on real hardware (it simply reboots).
  On real hardware only

  movl (%rcx), %ecx

  works (also in qemu).

  Commandline:
  qemu-system-x86_64 \
  		-kernel $LINUXDIR/arch/x86_64/boot/bzImage \
  		-hda $BUILDROOTDIR/output/images/rootfs.ext2 \
  		-append "root=/dev/sda rw rootfstype=ext2 maxcpus=4" \
  		-cpu phenom \
  		-smp 4 \
  		-gdb tcp::1234 \
  		-net nic -net user

  Guest:
  Vanilla Linux Kernel 2.6.37.6 64-bit with buildroot

  Mikael Pettersson from the linux kernel mailinglist told me it's an
  accepts-invalid bug in qemu.

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/796202/+subscriptions