linux-kernel - Re: [PATCH] powerpc/xive: Fix bogus error code returned by OPAL

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Message-ID: <87k1aezz78.fsf@mpe.ellerman.id.au>
Date:   Thu, 12 Sep 2019 00:26:19 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Greg Kurz <groug@...d.org>
Cc:     Paul Mackerras <paulus@...abs.org>,
        Cédric Le Goater <clg@...d.org>,
        David Gibson <david@...son.dropbear.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/xive: Fix bogus error code returned by OPAL

Hi Greg,

Couple of comments ...

Greg Kurz <groug@...d.org> writes:
> There's a bug in skiboot that causes the OPAL_XIVE_ALLOCATE_IRQ call
> to return the 32-bit value 0xffffffff when OPAL has run out of IRQs.
> Unfortunatelty, OPAL return values are signed 64-bit entities and
> errors are supposed to be negative. If that happens, the linux code
> confusingly treats 0xffffffff as a valid IRQ number and panics at some
> point.
>
> A fix was recently merged in skiboot:
>
> e97391ae2bb5 ("xive: fix return value of opal_xive_allocate_irq()")
>
> but we need a workaround anyway to support older skiboots already
> on the field.
  ^
  in
 
>
> Internally convert 0xffffffff to OPAL_RESOURCE which is the usual error
> returned upon resource exhaustion.

This should go to stable, any idea what versions it should go back to?
Probably whenever the xive code was introduced?

> Signed-off-by: Greg Kurz <groug@...d.org>
> ---
>  arch/powerpc/sysdev/xive/native.c |   13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/sysdev/xive/native.c b/arch/powerpc/sysdev/xive/native.c
> index 37987c815913..c35583f84f9f 100644
> --- a/arch/powerpc/sysdev/xive/native.c
> +++ b/arch/powerpc/sysdev/xive/native.c
> @@ -231,6 +231,15 @@ static bool xive_native_match(struct device_node *node)
>  	return of_device_is_compatible(node, "ibm,opal-xive-vc");
>  }
>  
> +static int64_t opal_xive_allocate_irq_fixup(uint32_t chip_id)
          ^                                    ^
          Can you use s64 here and u32 here ....

Instead of calling this opal_xive_allocate_irq_fixup() and relying on
all callers to call the fixup, can we rename the opal wrapper and leave
this function's name unchanged, eg:

-OPAL_CALL(opal_xive_allocate_irq,              OPAL_XIVE_ALLOCATE_IRQ);
+OPAL_CALL(opal_xive_allocate_irq_raw,          OPAL_XIVE_ALLOCATE_IRQ);


> +{
> +	s64 irq = opal_xive_allocate_irq(chip_id);
> +
> +#define XIVE_ALLOC_NO_SPACE	0xffffffff /* No possible space */
> +	return
> +		irq == XIVE_ALLOC_NO_SPACE ? OPAL_RESOURCE : irq;
> +}

I don't really like the #define and the weird indenting and so on, can
we instead do it like:

	/*
         * Old versions of skiboot can incorrectly return 0xffffffff to
         * indicate no space, fix it up here.
         */
	return irq == 0xffffffff ? OPAL_RESOURCE : irq;

cheers