[edk2-devel] [PATCH V7 36/37] UefiCpuPkg: Setting initial-count register as the last step
Lendacky, Thomas via groups.io
thomas.lendacky=amd.com at groups.io
Tue May 10 20:30:16 UTC 2022
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.yao at intel.com>
> Cc: Gerd Hoffmann <kraxel at redhat.com>
> Cc: Anthony Perard <anthony.perard at citrix.com>
> Cc: Julien Grall <julien at xen.org>
> Cc: Eric Dong <eric.dong at intel.com>
> Cc: Ray Ni <ray.ni at intel.com>
> Acked-by: Gerd Hoffmann <kraxel at redhat.com>
> Signed-off-by: Min Xu <min.m.xu at 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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