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Re: [PATCH 0/2] hw/acpi: bump MADT to revision 5
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From: |
Eric DeVolder |
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Subject: |
Re: [PATCH 0/2] hw/acpi: bump MADT to revision 5 |
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Date: |
Tue, 4 Apr 2023 09:52:09 -0500 |
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Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.1 |
I'm back from travel and catching up. More info below.
eric
On 3/31/23 11:25, Igor Mammedov wrote:
On Wed, 29 Mar 2023 12:47:05 -0400
"Michael S. Tsirkin" <mst@redhat.com> wrote:
On Wed, Mar 29, 2023 at 08:14:37AM -0500, Eric DeVolder wrote:
On 3/29/23 00:19, Michael S. Tsirkin wrote:
Hmm I don't think we can reasonably make such a change for 8.0.
Seems too risky.
Also, I feel we want to have an internal (with "x-" prefix") flag to
revert to old behaviour, in case of breakage on some guests. and maybe
we want to keep old revision for old machine types.
Ok, what option name, for keeping old behavior, would you like?
Don't much care. x-madt-rev?
if it works fine (cold & hot-plug) with older linux/windows guests
I'd rather avoid adding compat knob (we typically do that in ACPI tables
only when change breaks something).
(as old guest I'd define WinXP sp3 (/me wonders if we still care about
dead EOLed OS) perhaps WS2008 would be a better minimum target these days
and RHEL6 (or some older ACPI enabled kernel with hotplug support))
Thus far I've tested this patch series with the following guests. In both cases
below,
the guest started with -smp 8,maxcpus=16, and I simply attempted to hot plug
and unplug
cpu8, with: device_add id=cpu8 driver=host-x86_64-cpu socket-id=0 core-id=8
thread-id=0.
1) Windows Server 2008.
In Windows, after logging-in, I close the first full-screen window
and then "Server Manager" window pops up. I navigate to left hand
pane and choose Diagnostics -> Device Manager -> Processors.
I count them before and after.
When hotplugging a cpu, you can see the new processor show up in the
processor list. That is, it goes from 8 to 9.
When hot unplugging the CPU, Windows refuses:
The 'Intel(R) Xeon(R) CPU D-1533 @ 2.10GHz' device is not
removable and cannot be ejected or unplugged.
2) RHEL 6.9
From dmesg:
ACPI: APIC 000000007ffe32f0 000F0 (v05 BOCHS BXPC 00000001 BXPC 00000001)
SMP: Allowing 16 CPUs, 8 hotplug CPUs
# cat /sys/devices/system/cpu/online
0-7
(QEMU) device_add ...
CPU 8 got hotplugged
Booting Node 0 Processor 8 APIC 0x8
kvm-clock: cpu 8, msr 2830ed00
Will online and init hotplugged CPU: 8
microcode: CPU8 sig=0x50663, pf=0x1, revision=0x700001c
platform microcode: firmware: requesting intel-ucode/06-56-03
# cat /sys/devices/system/cpu/online
0-8
(QEMU) device_del ...
Broke affinity for irq 24
CPU 8 is now offline
# cat /sys/devices/system/cpu/online
0-7
RHEL 6.9
kernel 2.6.32-696.el6.x86_64
build Feb 21 2017
So with these two older guest OS, it appears to still work. If there are others to be tested, let me
know.
On Tue, Mar 28, 2023 at 11:59:24AM -0400, Eric DeVolder wrote:
The following Linux kernel change broke CPU hotplug for MADT revision
less than 5.
commit e2869bd7af60 ("x86/acpi/boot: Do not register processors that cannot be
onlined for x2APIC")
Presumably it's being fixed? Link to discussion? Patch fixing that in
Linux?
https://lore.kernel.org/linux-acpi/20230327191026.3454-1-eric.devolder@oracle.com/T/#t
Great! Maybe stick a Link: tag in the commit log.
Sure, will include that with v2.
So it's guest bug which is in process of being fixed.
(i.e. QEMU technically correct as long as MADT revision < 5)
Iiuc, if QEMU generates x2apic tables with .revision = 1, that is not correct
(as x2APIC shows up in .revision=3).
But if QEMU generates, apic, sapic, or x2apic tables with .revision = 5, that
is correct (as all are valid options thru .revision 5).
In this case I'd not touch x86 MADT at all (It should be upto
downstream distros to fix guest kernel).
Fwiw, this has been fixed and should show up in 6.3-rc6 this weekend.
Probably the same applies to ARM variant
i.e. we should bump rev only when current one gets in the way
(aka we are pulling in new fields/definitions from new version)
As part of the investigation into resolving this breakage, I learned
that i386 QEMU reports revision 1, while technically it is at revision 3.
(Arm QEMU reports revision 4, and that is valid/correct.)
ACPI 6.3 bumps MADT revision to 5 as it introduces an Online Capable
flag that the above Linux patch utilizes to denote hot pluggable CPUs.
So in order to bump MADT to the current revision of 5, need to
validate that all MADT table changes between 1 and 5 are present
in QEMU.
Below is a table summarizing the changes to the MADT. This information
gleamed from the ACPI specs on uefi.org.
ACPI MADT What
Version Version
1.0 MADT not present
2.0 1 Section 5.2.10.4
3.0 2 Section 5.2.11.4
5.2.11.13 Local SAPIC Structure added two new fields:
ACPI Processor UID Value
ACPI Processor UID String
5.2.10.14 Platform Interrupt Sources Structure:
Reserved changed to Platform Interrupt Sources Flags
3.0b 2 Section 5.2.11.4
Added a section describing guidelines for the ordering of
processors in the MADT to support proper boot processor
and multi-threaded logical processor operation.
4.0 3 Section 5.2.12
Adds Processor Local x2APIC structure type 9
Adds Local x2APIC NMI structure type 0xA
5.0 3 Section 5.2.12
6.0 3 Section 5.2.12
6.0a 4 Section 5.2.12
Adds ARM GIC structure types 0xB-0xF
6.2a 45 Section 5.2.12 <--- yep it says version 45!
6.2b 5 Section 5.2.12
GIC ITS last Reserved offset changed to 16 from 20 (typo)
6.3 5 Section 5.2.12
Adds Local APIC Flags Online Capable!
Adds GICC SPE Overflow Interrupt field
6.4 5 Section 5.2.12
Adds Multiprocessor Wakeup Structure type 0x10
(change notes says structure previously misplaced?)
6.5 5 Section 5.2.12
For the MADT revision change 1 -> 2, the spec has a change to the
SAPIC structure. In general, QEMU does not generate/support SAPIC.
So the QEMU i386 MADT revision can safely be moved to 2.
For the MADT revision change 2 -> 3, the spec adds Local x2APIC
structures. QEMU has long supported x2apic ACPI structures. A simple
search of x2apic within QEMU source and hw/i386/acpi-common.c
specifically reveals this.
But not unconditionally.
I don't think that reporting revision 3 requires that generation of x2apic;
one could still see apic, x2apic, or sapic in theory. I realize qemu doesn't
do sapic...
So the QEMU i386 MADT revision can safely
be moved to 3.
For the MADT revision change 3 -> 4, the spec adds support for the ARM
GIC structures. QEMU ARM does in fact generate and report revision 4.
As these will not be used by i386 QEMU, so then the QEMU i386 MADT
revision can safely be moved to 4 as well.
Now for the MADT revision change 4 -> 5, the spec adds the Online
Capable flag to the Local APIC structure, and the ARM GICC SPE
Overflow Interrupt field.
For the ARM SPE, an existing 3-byte Reserved field is broken into a 1-
byte Reserved field and a 2-byte SPE field. The spec says that is SPE
Overflow is not supported, it should be zero.
For the i386 Local APIC flag Online Capable, the spec has certain rules
about this value. And in particuar setting this value now explicitly
indicates a hotpluggable CPU.
So this patch makes the needed changes to move both ARM and i386 MADT
to revision 5. These are not complicated, thankfully.
Without these changes, the information below shows "how" CPU hotplug
breaks with the current upstream Linux kernel 6.3. For example, a Linux
guest started with:
qemu-system-x86_64 -smp 30,maxcpus=32 ...
and then attempting to hotplug a CPU:
(QEMU) device_add id=cpu30 driver=host-x86_64-cpu socket-id=0 core-id=30
thread-id=0
fails with the following:
APIC: NR_CPUS/possible_cpus limit of 30 reached. Processor 30/0x.
ACPI: Unable to map lapic to logical cpu number
acpi LNXCPU:1e: Enumeration failure
# dmesg | grep smpboot
smpboot: Allowing 30 CPUs, 0 hotplug CPUs
smpboot: CPU0: Intel(R) Xeon(R) CPU D-1533 @ 2.10GHz (family: 0x)
smpboot: Max logical packages: 1
smpboot: Total of 30 processors activated (125708.76 BogoMIPS)
# iasl -d /sys/firmware/tables/acpi/APIC
[000h 0000 4] Signature : "APIC" [Multiple APIC
Descript
[004h 0004 4] Table Length : 00000170
[008h 0008 1] Revision : 01 <=====
[009h 0009 1] Checksum : 9C
[00Ah 0010 6] Oem ID : "BOCHS "
[010h 0016 8] Oem Table ID : "BXPC "
[018h 0024 4] Oem Revision : 00000001
[01Ch 0028 4] Asl Compiler ID : "BXPC"
[020h 0032 4] Asl Compiler Revision : 00000001
...
[114h 0276 1] Subtable Type : 00 [Processor Local APIC]
[115h 0277 1] Length : 08
[116h 0278 1] Processor ID : 1D
[117h 0279 1] Local Apic ID : 1D
[118h 0280 4] Flags (decoded below) : 00000001
Processor Enabled : 1 <=====
[11Ch 0284 1] Subtable Type : 00 [Processor Local APIC]
[11Dh 0285 1] Length : 08
[11Eh 0286 1] Processor ID : 1E
[11Fh 0287 1] Local Apic ID : 1E
[120h 0288 4] Flags (decoded below) : 00000000
Processor Enabled : 0 <=====
[124h 0292 1] Subtable Type : 00 [Processor Local APIC]
[125h 0293 1] Length : 08
[126h 0294 1] Processor ID : 1F
[127h 0295 1] Local Apic ID : 1F
[128h 0296 4] Flags (decoded below) : 00000000
Processor Enabled : 0 <=====
The (latest upstream) Linux kernel sees 30 Enabled processors, and
does not consider processors 31 and 32 to be hotpluggable.
With this patch series applied, by bumping MADT to revision 5, the
latest upstream Linux kernel correctly identifies 30 CPUs plus 2
hotpluggable CPUS.
CPU30 has been hot-added
smpboot: Booting Node 0 Processor 30 APIC 0x1e
Will online and init hotplugged CPU: 30
# dmesg | grep smpboot
smpboot: Allowing 32 CPUs, 2 hotplug CPUs
smpboot: CPU0: Intel(R) Xeon(R) CPU D-1533 @ 2.10GHz (family: 0x6, model:
0x56, stepping: 0x3)
smpboot: Max logical packages: 2
smpboot: Total of 30 processors activated (125708.76 BogoMIPS)
# iasl -d /sys/firmware/tables/acpi/APIC
[000h 0000 004h] Signature : "APIC" [Multiple APIC
Descript
[004h 0004 004h] Table Length : 00000170
[008h 0008 001h] Revision : 05 <=====
[009h 0009 001h] Checksum : 94
[00Ah 0010 006h] Oem ID : "BOCHS "
[010h 0016 008h] Oem Table ID : "BXPC "
[018h 0024 004h] Oem Revision : 00000001
[01Ch 0028 004h] Asl Compiler ID : "BXPC"
[020h 0032 004h] Asl Compiler Revision : 00000001
...
[114h 0276 001h] Subtable Type : 00 [Processor Local APIC]
[115h 0277 001h] Length : 08
[116h 0278 001h] Processor ID : 1D
[117h 0279 001h] Local Apic ID : 1D
[118h 0280 004h] Flags (decoded below) : 00000001
Processor Enabled : 1 <=====
Runtime Online Capable : 0 <=====
[11Ch 0284 001h] Subtable Type : 00 [Processor Local APIC]
[11Dh 0285 001h] Length : 08
[11Eh 0286 001h] Processor ID : 1E
[11Fh 0287 001h] Local Apic ID : 1E
[120h 0288 004h] Flags (decoded below) : 00000002
Processor Enabled : 0 <=====
Runtime Online Capable : 1 <=====
[124h 0292 001h] Subtable Type : 00 [Processor Local APIC]
[125h 0293 001h] Length : 08
[126h 0294 001h] Processor ID : 1F
[127h 0295 001h] Local Apic ID : 1F
[128h 0296 004h] Flags (decoded below) : 00000002
Processor Enabled : 0 <=====
Runtime Online Capable : 1 <=====
Regards,
Eric
Can you please report which guests were tested?
I've been using primarily upstream Linux. Kernels at and before 6.2.0 didn't
have the "broken" patch mentioned above, and worked (for the reasons cited
in the patch discussion to "fix" that patch). Any kernel since has the
"broken" patch and will exhibit the issue.
I've been using q35.
If there are other samples you'd like to see, let me know and I'll try.
Also, my responses will be delayed as I'm traveling the remainder of the week.
Thanks!
eric
As a minimum some windows versions. The older the better.
Eric DeVolder (2):
hw/acpi: arm: bump MADT to revision 5
hw/acpi: i386: bump MADT to revision 5
hw/arm/virt-acpi-build.c | 6 ++++--
hw/i386/acpi-common.c | 13 ++++++++++---
2 files changed, 14 insertions(+), 5 deletions(-)
--
2.31.1
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