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

["Ard Biesheuvel" <ardb@kernel.org>]

Merged as #1920

Thanks all,


On Thu, 26 Aug 2021 at 04:47, gaoliming <gaoliming@byosoft.com.cn> wrote:
>
> 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
> > >
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