回复: [edk2-devel] [PATCH] ArmPkg/GicV3Dxe: Don't signal EOI on arbitrary interrupts

["gaoliming" <gaoliming@byosoft.com.cn>]

I agree with Leif.

Thanks
Liming
> -----邮件原件-----
> 发件人: devel@edk2.groups.io <devel@edk2.groups.io> 代表 Leif Lindholm
> 发送时间: 2021年8月25日 20:51
> 收件人: Ard Biesheuvel <ardb@kernel.org>
> 抄送: devel@edk2.groups.io; sami.mujawar@arm.com;
> gaoliming@byosoft.com.cn; Marc Zyngier <maz@kernel.org>
> 主题: Re: [edk2-devel] [PATCH] ArmPkg/GicV3Dxe: Don't signal EOI on
> arbitrary interrupts
> 
> On Tue, Aug 24, 2021 at 17:31:32 +0200, Ard Biesheuvel wrote:
> > Currently, at ExitBootServices() time, the GICv3 driver signals
> > End-Of-Interrupt (EOI) on all interrupt lines that are supported by the
> > interrupt controller. This appears to have been carried over from the
> > GICv2 version, but has been turned into something that violates the GIC
> > spec, and may trigger SError exceptions on some implementations.
> >
> > Marc puts it as follows:
> >
> >   The GIC interrupt state machine is pretty strict. An interrupt can
> >   only be deactivated (with or without prior priority drop) if it has
> >   been acknowledged first. In GIC speak, this means that only the
> >   following sequences are valid:
> >
> >   With EOImode==0:
> > 	  x = ICC_IAR{0,1}_EL1;
> > 	  ICC_EOIR{0,1}_EL1 = x;
> >
> >   With EOImode==1:
> > 	  x = ICC_IAR{0,1}_EL1;
> > 	  ICC_EOIR{0,1}_EL1 = x;
> > 	  ICC_DIR_EL1 = x;
> >
> >   Any write to ICC_EOIR{0,1}_EL1 that isn't the direct consequence of
> >   the same value being read from ICC_IAR{0,1}_EL1, and with the correct
> >   nesting, breaks the state machine and leads to unpredictable results
> >   that affects *all* interrupts in the system (most likely, the priority
> >   system is dead). See Figure 4-3 ("Interrupt handling state machine")
> >   in Arm IHI 0069F for a description of the acceptable transitions.
> >
> >   Additionally, on implementations that have ICC_CTLR_EL1.SEIS==1, a
> >   SError may be generated to signal the error. See the various
> >
> >   <quote>
> > 	  IMPLEMENTATION_DEFINED "SError ....";
> >   </quote>
> >
> >   that are all over the pseudocode contained in the same architecture
> >   spec. Needless to say, this is pretty final for any SW that would do
> >   silly things on such implementations (which do exist).
> >
> > Given that in our implementation, every signalled interrupt is acked,
> > handled and EOId in sequence, there is no reason to EOI all interrupts
> > at ExitBootServices() time in the first place, so let's just drop this
> > code. This fixes an issue reported by Marc where an SError is triggered
> > by this code, bringing down the system.
> >
> > Reported-by: Marc Zyngier <maz@kernel.org>
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> 
> Yikes.
> Pretty sure that wasn't the right thing to do on gicv2 either.
> 
> Reviewed-by: Leif Lindholm <leif@nuviainc.com>
> 
> > ---
> > This is a clear bugfix, but given how late we are in the cycle, I will
> > leave it up to Liming to decide whether we can still take this for the
> > upcoming stable tag.
> 
> I can see hypothetical situations where this could break existing
> (broken) firmware ... so I would prefer to leave it until after the
> stable tag unless there is substantial benefit to including it here.
> 
> /
>     Leif
> 
> >  ArmPkg/Drivers/ArmGic/GicV3/ArmGicV3Dxe.c | 4 ----
> >  1 file changed, 4 deletions(-)
> >
> > diff --git a/ArmPkg/Drivers/ArmGic/GicV3/ArmGicV3Dxe.c
> b/ArmPkg/Drivers/ArmGic/GicV3/ArmGicV3Dxe.c
> > index 85ee4c87b6d1..fa515d1a01ba 100644
> > --- a/ArmPkg/Drivers/ArmGic/GicV3/ArmGicV3Dxe.c
> > +++ b/ArmPkg/Drivers/ArmGic/GicV3/ArmGicV3Dxe.c
> > @@ -344,10 +344,6 @@ GicV3ExitBootServicesEvent (
> >      GicV3DisableInterruptSource (&gHardwareInterruptV3Protocol,
> Index);
> >    }
> >
> > -  for (Index = 0; Index < mGicNumInterrupts; Index++) {
> > -    GicV3EndOfInterrupt (&gHardwareInterruptV3Protocol, Index);
> > -  }
> > -
> >    // Disable Gic Interface
> >    ArmGicV3DisableInterruptInterface ();
> >
> > --
> > 2.30.2
> >
> 
> 
> 
>