On 5/10/22 21:00, Xu, Min M wrote:
On May 11, 2022 4:30 AM, Tom Lendacky wrote:
On 2/28/22 01:21, Min Xu via groups.io wrote:
BZ:
https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.tianocore.org%2Fshow_bug.cgi%3Fid%3D3711&data=05%7C01%7Cthomas.lendacky%40amd.com%7Cce8cd76e1b054fe277d808da32f20976%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637878312370633666%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=C%2F0BMTV%2FoZdUxLwRbqzjNVdlMvEKfl20z6RwKeMzr2c%3D&reserved=0
Per SDM, changing the mode of APIC timer (from one-shot to periodic or
vice versa) by writing to the timer LVT entry does not start the timer.
To start the timer, it is necessary to write to the initial-count
register.
If initial-count is wrote before mode change, it's possible that timer
expired before the mode change. Thus failing the periodic mode.
I'm replying to this patch since I can't find patch V12 46/47 anywhere in my
email.
I've bisected a regression in the Linux kernel to this patch when an SEV-SNP
guest is booted. The following message is issued in the kernel for every AP
being brought online:
APIC: Stale IRR:
00000000,00000000,00000000,00000000,00000000,00000000,00000000,000
00020 ISR:
00000000,00000000,00000000,00000000,00000000,00000000,00000000,000
00000
Possibly a timing issue involving the mode switch with the interrupt
unmasked. If I leave the interrupt masked and only un-mask it after the
programming of the init-count, then the message goes away.
Do you mean in InitializeApicTimer, it should follow below steps:
1. mask LvtTimer. (set LvtTimer.Bits.Mask = 1)
2. Do other stuff, including programing the init-count register.
3. un-mask LvtTimer (set LvtTimer.Bit.Mask = 0)
Yes, I believe so. I'm not an expert on the APIC timer, but that seems
reasonable to me.
Thanks,
Tom
Thanks
Min
-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#89682): https://edk2.groups.io/g/devel/message/89682
Mute This Topic: https://groups.io/mt/89446188/21656
Group Owner: devel+ow...@edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [arch...@mail-archive.com]
-=-=-=-=-=-=-=-=-=-=-=-
