On 2/28/22 01:21, Min Xu via groups.io wrote:
BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3711
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:
00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000020 ISR:
00000000,00000000,00000000,00000000,00000000,00000000,00000000,00000000
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.
Thoughts?
Thanks,
Tom
Cc: Jiewen Yao <jiewen....@intel.com>
Cc: Gerd Hoffmann <kra...@redhat.com>
Cc: Anthony Perard <anthony.per...@citrix.com>
Cc: Julien Grall <jul...@xen.org>
Cc: Eric Dong <eric.d...@intel.com>
Cc: Ray Ni <ray...@intel.com>
Acked-by: Gerd Hoffmann <kra...@redhat.com>
Signed-off-by: Min Xu <min.m...@intel.com>
---
.../Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c
b/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c
index 2d17177df12b..f26d9c93894f 100644
--- a/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c
+++ b/UefiCpuPkg/Library/BaseXApicX2ApicLib/BaseXApicX2ApicLib.c
@@ -967,11 +967,6 @@ InitializeApicTimer (
//
InitializeLocalApicSoftwareEnable (TRUE);
- //
- // Program init-count register.
- //
- WriteLocalApicReg (XAPIC_TIMER_INIT_COUNT_OFFSET, InitCount);
-
if (DivideValue != 0) {
ASSERT (DivideValue <= 128);
ASSERT (DivideValue == GetPowerOfTwo32 ((UINT32)DivideValue));
@@ -996,6 +991,11 @@ InitializeApicTimer (
LvtTimer.Bits.Mask = 0;
LvtTimer.Bits.Vector = Vector;
WriteLocalApicReg (XAPIC_LVT_TIMER_OFFSET, LvtTimer.Uint32);
+
+ //
+ // Program init-count register.
+ //
+ WriteLocalApicReg (XAPIC_TIMER_INIT_COUNT_OFFSET, InitCount);
}
/**
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