[Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Peng Fan]

The end should be GICD_ISACTIVERN not GICD_ISACTIVER,
and also print a warning for the unhandled read.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
---

V2:
 Add a warning message

 xen/arch/arm/vgic-v3.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/vgic-v3.c b/xen/arch/arm/vgic-v3.c
index 422b94f902..a15b9f6441 100644
--- a/xen/arch/arm/vgic-v3.c
+++ b/xen/arch/arm/vgic-v3.c
@@ -706,7 +706,10 @@ static int __vgic_v3_distr_common_mmio_read(const char *name, struct vcpu *v,
         goto read_as_zero;
 
     /* Read the active status of an IRQ via GICD/GICR is not supported */
-    case VRANGE32(GICD_ISACTIVER, GICD_ISACTIVER):
+    case VRANGE32(GICD_ISACTIVER, GICD_ISACTIVERN):
+        printk(XENLOG_G_ERR "%pv: vGICD: unhandled read from ISACTIVER%d\n",
+               v, (reg - GICD_ISACTIVER) / 4);
+        goto read_as_zero;
     case VRANGE32(GICD_ICACTIVER, GICD_ICACTIVERN):
         goto read_as_zero;
 
-- 
2.16.4


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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Stefano Stabellini]

On Fri, 22 Nov 2019, Peng Fan wrote:
> The end should be GICD_ISACTIVERN not GICD_ISACTIVER,
> and also print a warning for the unhandled read.
> 
> Signed-off-by: Peng Fan <peng.fan@nxp.com>
> ---
> 
> V2:
>  Add a warning message
> 
>  xen/arch/arm/vgic-v3.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/arm/vgic-v3.c b/xen/arch/arm/vgic-v3.c
> index 422b94f902..a15b9f6441 100644
> --- a/xen/arch/arm/vgic-v3.c
> +++ b/xen/arch/arm/vgic-v3.c
> @@ -706,7 +706,10 @@ static int __vgic_v3_distr_common_mmio_read(const char *name, struct vcpu *v,
>          goto read_as_zero;
>  
>      /* Read the active status of an IRQ via GICD/GICR is not supported */
> -    case VRANGE32(GICD_ISACTIVER, GICD_ISACTIVER):
> +    case VRANGE32(GICD_ISACTIVER, GICD_ISACTIVERN):
> +        printk(XENLOG_G_ERR "%pv: vGICD: unhandled read from ISACTIVER%d\n",
> +               v, (reg - GICD_ISACTIVER) / 4);

All the other similar printks that we have in vgic-v3.c don't have the
"/ 4", for instance:

    case VRANGE32(GICD_ISACTIVER, GICD_ISACTIVERN):
        if ( dabt.size != DABT_WORD ) goto bad_width;
        printk(XENLOG_G_ERR
               "%pv: %s: unhandled word write %#"PRIregister" to ISACTIVER%d\n",
               v, name, r, reg - GICD_ISACTIVER);

However, reg reflects the address of the register, so actually, the
division by 4 looks correct if we want to get the index of the specific
register. Thanks for spotting this. We'll need to do a clean-up in the
file later.

Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>



> +        goto read_as_zero;
>      case VRANGE32(GICD_ICACTIVER, GICD_ICACTIVERN):
>          goto read_as_zero;
>  
> -- 
> 2.16.4
> 

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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Stefano Stabellini]

+ Juergen

I missed that you weren't in CC to the original patch, sorry.
I think this patch should go in, as otherwise Linux 5.4 could run into
problems. It is also a pretty straightforward 4 lines patch.



On Fri, 22 Nov 2019, Stefano Stabellini wrote:
> On Fri, 22 Nov 2019, Peng Fan wrote:
> > The end should be GICD_ISACTIVERN not GICD_ISACTIVER,
> > and also print a warning for the unhandled read.
> > 
> > Signed-off-by: Peng Fan <peng.fan@nxp.com>
> > ---
> > 
> > V2:
> >  Add a warning message
> > 
> >  xen/arch/arm/vgic-v3.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/xen/arch/arm/vgic-v3.c b/xen/arch/arm/vgic-v3.c
> > index 422b94f902..a15b9f6441 100644
> > --- a/xen/arch/arm/vgic-v3.c
> > +++ b/xen/arch/arm/vgic-v3.c
> > @@ -706,7 +706,10 @@ static int __vgic_v3_distr_common_mmio_read(const char *name, struct vcpu *v,
> >          goto read_as_zero;
> >  
> >      /* Read the active status of an IRQ via GICD/GICR is not supported */
> > -    case VRANGE32(GICD_ISACTIVER, GICD_ISACTIVER):
> > +    case VRANGE32(GICD_ISACTIVER, GICD_ISACTIVERN):
> > +        printk(XENLOG_G_ERR "%pv: vGICD: unhandled read from ISACTIVER%d\n",
> > +               v, (reg - GICD_ISACTIVER) / 4);
> 
> All the other similar printks that we have in vgic-v3.c don't have the
> "/ 4", for instance:
> 
>     case VRANGE32(GICD_ISACTIVER, GICD_ISACTIVERN):
>         if ( dabt.size != DABT_WORD ) goto bad_width;
>         printk(XENLOG_G_ERR
>                "%pv: %s: unhandled word write %#"PRIregister" to ISACTIVER%d\n",
>                v, name, r, reg - GICD_ISACTIVER);
> 
> However, reg reflects the address of the register, so actually, the
> division by 4 looks correct if we want to get the index of the specific
> register. Thanks for spotting this. We'll need to do a clean-up in the
> file later.
> 
> Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
> 
> 
> 
> > +        goto read_as_zero;
> >      case VRANGE32(GICD_ICACTIVER, GICD_ICACTIVERN):
> >          goto read_as_zero;


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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Julien Grall]

Hi,

On 26/11/2019 20:43, Stefano Stabellini wrote:
> + Juergen
> 
> I missed that you weren't in CC to the original patch, sorry.
> I think this patch should go in, as otherwise Linux 5.4 could run into
> problems. It is also a pretty straightforward 4 lines patch.

5.5 (or 5.6) is not going to run on Xen for other reasons (still in the 
vGIC)... So I would not view this as critical.

Cheers,

-- 
Julien Grall

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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Stefano Stabellini]

On Tue, 26 Nov 2019, Julien Grall wrote:
> Hi,
> 
> On 26/11/2019 20:43, Stefano Stabellini wrote:
> > + Juergen
> > 
> > I missed that you weren't in CC to the original patch, sorry.
> > I think this patch should go in, as otherwise Linux 5.4 could run into
> > problems. It is also a pretty straightforward 4 lines patch.
> 
> 5.5 (or 5.6) is not going to run on Xen for other reasons (still in the
> vGIC)... So I would not view this as critical.

5.5 is not out yet, in fact, the dev window has just opened. Isn't your
statement a bit premature?

In any case, even if potential future Linux releases could have other
additional issues, I don't think it should change our current view on
this specific issue which affects 5.4, just released.

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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Julien Grall]

Hi,

On 26/11/2019 23:17, Stefano Stabellini wrote:
> On Tue, 26 Nov 2019, Julien Grall wrote:
>> Hi,
>>
>> On 26/11/2019 20:43, Stefano Stabellini wrote:
>>> + Juergen
>>>
>>> I missed that you weren't in CC to the original patch, sorry.
>>> I think this patch should go in, as otherwise Linux 5.4 could run into
>>> problems. It is also a pretty straightforward 4 lines patch.
>>
>> 5.5 (or 5.6) is not going to run on Xen for other reasons (still in the
>> vGIC)... So I would not view this as critical.
> 
> 5.5 is not out yet, in fact, the dev window has just opened. Isn't your
> statement a bit premature?

The GICv4.1 work [1] is going to prevent Linux booting on all current 
versions of Xen. While I can't confirm this is going to be merged in 
5.5, I can tell you this will break.

> 
> In any case, even if potential future Linux releases could have other
> additional issues, I don't think it should change our current view on
> this specific issue which affects 5.4, just released.

The patch is definitely not as straightforward as you may think. Please 
refer to the discussion we had on the first version. I voiced concern 
about this approach and gave point what could go wrong with happen.

This patch may be better than the current state (i.e crashing), but this 
wasn't tested enough to confirm this is the correct things to do and no 
other bug will appear (I don't believe reading I*ACTIVER was ever tested 
before).

It is an annoying bug, but this is only affecting 5.4 which has just 
been released. It feels to me this is a fairly risky choice to merge it 
qutie late in the release without a good graps of the problem (see above).

So I would definitly, prefer if this patch is getting through backport 
once we get more testing.

We can still document the bug in the release note and point people to 
the patch.

Anyway, this is Juergen choice here. But at least now he has the full 
picture...

Cheers,

[1] https://lwn.net/Articles/800494/

-- 
Julien Grall

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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Jürgen Groß]

On 27.11.19 01:01, Julien Grall wrote:
> Hi,
> 
> On 26/11/2019 23:17, Stefano Stabellini wrote:
>> On Tue, 26 Nov 2019, Julien Grall wrote:
>>> Hi,
>>>
>>> On 26/11/2019 20:43, Stefano Stabellini wrote:
>>>> + Juergen
>>>>
>>>> I missed that you weren't in CC to the original patch, sorry.
>>>> I think this patch should go in, as otherwise Linux 5.4 could run into
>>>> problems. It is also a pretty straightforward 4 lines patch.
>>>
>>> 5.5 (or 5.6) is not going to run on Xen for other reasons (still in the
>>> vGIC)... So I would not view this as critical.
>>
>> 5.5 is not out yet, in fact, the dev window has just opened. Isn't your
>> statement a bit premature?
> 
> The GICv4.1 work [1] is going to prevent Linux booting on all current 
> versions of Xen. While I can't confirm this is going to be merged in 
> 5.5, I can tell you this will break.
> 
>>
>> In any case, even if potential future Linux releases could have other
>> additional issues, I don't think it should change our current view on
>> this specific issue which affects 5.4, just released.
> 
> The patch is definitely not as straightforward as you may think. Please 
> refer to the discussion we had on the first version. I voiced concern 
> about this approach and gave point what could go wrong with happen.
> 
> This patch may be better than the current state (i.e crashing), but this 
> wasn't tested enough to confirm this is the correct things to do and no 
> other bug will appear (I don't believe reading I*ACTIVER was ever tested 
> before).
> 
> It is an annoying bug, but this is only affecting 5.4 which has just 
> been released. It feels to me this is a fairly risky choice to merge it 
> qutie late in the release without a good graps of the problem (see above).
> 
> So I would definitly, prefer if this patch is getting through backport 
> once we get more testing.
> 
> We can still document the bug in the release note and point people to 
> the patch.
> 
> Anyway, this is Juergen choice here. But at least now he has the full 
> picture...
> 
> Cheers,
> 
> [1] https://lwn.net/Articles/800494/
> 

Thanks, Julien, for sharing your opinion.

With that statement I'd like to defer this patch to 4.14.


Juergen

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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Peng Fan]

> Subject: Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER
> range
> 
> On 27.11.19 01:01, Julien Grall wrote:
> > Hi,
> >
> > On 26/11/2019 23:17, Stefano Stabellini wrote:
> >> On Tue, 26 Nov 2019, Julien Grall wrote:
> >>> Hi,
> >>>
> >>> On 26/11/2019 20:43, Stefano Stabellini wrote:
> >>>> + Juergen
> >>>>
> >>>> I missed that you weren't in CC to the original patch, sorry.
> >>>> I think this patch should go in, as otherwise Linux 5.4 could run
> >>>> into problems. It is also a pretty straightforward 4 lines patch.
> >>>
> >>> 5.5 (or 5.6) is not going to run on Xen for other reasons (still in
> >>> the vGIC)... So I would not view this as critical.
> >>
> >> 5.5 is not out yet, in fact, the dev window has just opened. Isn't
> >> your statement a bit premature?
> >
> > The GICv4.1 work [1] is going to prevent Linux booting on all current
> > versions of Xen. While I can't confirm this is going to be merged in
> > 5.5, I can tell you this will break.
> >
> >>
> >> In any case, even if potential future Linux releases could have other
> >> additional issues, I don't think it should change our current view on
> >> this specific issue which affects 5.4, just released.
> >
> > The patch is definitely not as straightforward as you may think.
> > Please refer to the discussion we had on the first version. I voiced
> > concern about this approach and gave point what could go wrong with
> happen.
> >
> > This patch may be better than the current state (i.e crashing), but
> > this wasn't tested enough to confirm this is the correct things to do
> > and no other bug will appear (I don't believe reading I*ACTIVER was
> > ever tested before).
> >
> > It is an annoying bug, but this is only affecting 5.4 which has just
> > been released. It feels to me this is a fairly risky choice to merge
> > it qutie late in the release without a good graps of the problem (see above).
> >
> > So I would definitly, prefer if this patch is getting through backport
> > once we get more testing.
> >
> > We can still document the bug in the release note and point people to
> > the patch.
> >
> > Anyway, this is Juergen choice here. But at least now he has the full
> > picture...
> >
> > Cheers,
> >
> > [1]
> > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flwn.
> >
> net%2FArticles%2F800494%2F&data=02%7C01%7Cpeng.fan%40nxp.co
> m%7Cdca
> >
> dfb39240749ee675e08d772fcd3ba%7C686ea1d3bc2b4c6fa92cd99c5c30163
> 5%7C0%7
> >
> C0%7C637104302519996592&sdata=7Jv2IhI8HZgBTSuYzkEplFyhX1lzmv
> d73xb5
> > 2d6ERVQ%3D&reserved=0
> >
> 
> Thanks, Julien, for sharing your opinion.
> 
> With that statement I'd like to defer this patch to 4.14.

But without this patch, 5.4 kernel will crash. So you prefer
we develop the solution as Julien suggested for 4.13?

Thanks,
Peng.

> 
> 
> Juergen
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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Jürgen Groß]

On 27.11.19 10:31, Peng Fan wrote:
>> Subject: Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER
>> range
>>
>> On 27.11.19 01:01, Julien Grall wrote:
>>> Hi,
>>>
>>> On 26/11/2019 23:17, Stefano Stabellini wrote:
>>>> On Tue, 26 Nov 2019, Julien Grall wrote:
>>>>> Hi,
>>>>>
>>>>> On 26/11/2019 20:43, Stefano Stabellini wrote:
>>>>>> + Juergen
>>>>>>
>>>>>> I missed that you weren't in CC to the original patch, sorry.
>>>>>> I think this patch should go in, as otherwise Linux 5.4 could run
>>>>>> into problems. It is also a pretty straightforward 4 lines patch.
>>>>>
>>>>> 5.5 (or 5.6) is not going to run on Xen for other reasons (still in
>>>>> the vGIC)... So I would not view this as critical.
>>>>
>>>> 5.5 is not out yet, in fact, the dev window has just opened. Isn't
>>>> your statement a bit premature?
>>>
>>> The GICv4.1 work [1] is going to prevent Linux booting on all current
>>> versions of Xen. While I can't confirm this is going to be merged in
>>> 5.5, I can tell you this will break.
>>>
>>>>
>>>> In any case, even if potential future Linux releases could have other
>>>> additional issues, I don't think it should change our current view on
>>>> this specific issue which affects 5.4, just released.
>>>
>>> The patch is definitely not as straightforward as you may think.
>>> Please refer to the discussion we had on the first version. I voiced
>>> concern about this approach and gave point what could go wrong with
>> happen.
>>>
>>> This patch may be better than the current state (i.e crashing), but
>>> this wasn't tested enough to confirm this is the correct things to do
>>> and no other bug will appear (I don't believe reading I*ACTIVER was
>>> ever tested before).
>>>
>>> It is an annoying bug, but this is only affecting 5.4 which has just
>>> been released. It feels to me this is a fairly risky choice to merge
>>> it qutie late in the release without a good graps of the problem (see above).
>>>
>>> So I would definitly, prefer if this patch is getting through backport
>>> once we get more testing.
>>>
>>> We can still document the bug in the release note and point people to
>>> the patch.
>>>
>>> Anyway, this is Juergen choice here. But at least now he has the full
>>> picture...
>>>
>>> Cheers,
>>>
>>> [1]
>>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flwn.
>>>
>> net%2FArticles%2F800494%2F&data=02%7C01%7Cpeng.fan%40nxp.co
>> m%7Cdca
>>>
>> dfb39240749ee675e08d772fcd3ba%7C686ea1d3bc2b4c6fa92cd99c5c30163
>> 5%7C0%7
>>>
>> C0%7C637104302519996592&sdata=7Jv2IhI8HZgBTSuYzkEplFyhX1lzmv
>> d73xb5
>>> 2d6ERVQ%3D&reserved=0
>>>
>>
>> Thanks, Julien, for sharing your opinion.
>>
>> With that statement I'd like to defer this patch to 4.14.
> 
> But without this patch, 5.4 kernel will crash. So you prefer
> we develop the solution as Julien suggested for 4.13?

I certainly won't take a patch for 4.13 when a maintainer of the
related code has reservations against it.

I think the best thing to do is to develop a proper patch the
maintainers are happy with and don't try to force it into 4.13 now.
Such a patch can still be backported to 4.13 later.


Juergen

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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Peng Fan]

> Subject: Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER
> range
> 
> On 27.11.19 10:31, Peng Fan wrote:
> >> Subject: Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix
> >> GICD_ISACTIVER range
> >>
> >> On 27.11.19 01:01, Julien Grall wrote:
> >>> Hi,
> >>>
> >>> On 26/11/2019 23:17, Stefano Stabellini wrote:
> >>>> On Tue, 26 Nov 2019, Julien Grall wrote:
> >>>>> Hi,
> >>>>>
> >>>>> On 26/11/2019 20:43, Stefano Stabellini wrote:
> >>>>>> + Juergen
> >>>>>>
> >>>>>> I missed that you weren't in CC to the original patch, sorry.
> >>>>>> I think this patch should go in, as otherwise Linux 5.4 could run
> >>>>>> into problems. It is also a pretty straightforward 4 lines patch.
> >>>>>
> >>>>> 5.5 (or 5.6) is not going to run on Xen for other reasons (still
> >>>>> in the vGIC)... So I would not view this as critical.
> >>>>
> >>>> 5.5 is not out yet, in fact, the dev window has just opened. Isn't
> >>>> your statement a bit premature?
> >>>
> >>> The GICv4.1 work [1] is going to prevent Linux booting on all
> >>> current versions of Xen. While I can't confirm this is going to be
> >>> merged in 5.5, I can tell you this will break.
> >>>
> >>>>
> >>>> In any case, even if potential future Linux releases could have
> >>>> other additional issues, I don't think it should change our current
> >>>> view on this specific issue which affects 5.4, just released.
> >>>
> >>> The patch is definitely not as straightforward as you may think.
> >>> Please refer to the discussion we had on the first version. I voiced
> >>> concern about this approach and gave point what could go wrong with
> >> happen.
> >>>
> >>> This patch may be better than the current state (i.e crashing), but
> >>> this wasn't tested enough to confirm this is the correct things to
> >>> do and no other bug will appear (I don't believe reading I*ACTIVER
> >>> was ever tested before).
> >>>
> >>> It is an annoying bug, but this is only affecting 5.4 which has just
> >>> been released. It feels to me this is a fairly risky choice to merge
> >>> it qutie late in the release without a good graps of the problem (see
> above).
> >>>
> >>> So I would definitly, prefer if this patch is getting through
> >>> backport once we get more testing.
> >>>
> >>> We can still document the bug in the release note and point people
> >>> to the patch.
> >>>
> >>> Anyway, this is Juergen choice here. But at least now he has the
> >>> full picture...
> >>>
> >>> Cheers,
> >>>
> >>> [1]
> >>>
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flwn.
> >>>
> >>
> net%2FArticles%2F800494%2F&data=02%7C01%7Cpeng.fan%40nxp.co
> >> m%7Cdca
> >>>
> >>
> dfb39240749ee675e08d772fcd3ba%7C686ea1d3bc2b4c6fa92cd99c5c30163
> >> 5%7C0%7
> >>>
> >>
> C0%7C637104302519996592&sdata=7Jv2IhI8HZgBTSuYzkEplFyhX1lzmv
> >> d73xb5
> >>> 2d6ERVQ%3D&reserved=0
> >>>
> >>
> >> Thanks, Julien, for sharing your opinion.
> >>
> >> With that statement I'd like to defer this patch to 4.14.
> >
> > But without this patch, 5.4 kernel will crash. So you prefer we
> > develop the solution as Julien suggested for 4.13?
> 
> I certainly won't take a patch for 4.13 when a maintainer of the related code
> has reservations against it.
> 
> I think the best thing to do is to develop a proper patch the maintainers are
> happy with and don't try to force it into 4.13 now.
> Such a patch can still be backported to 4.13 later.

Ok.

Julien,

What's your suggestion to fix the issue? Do you have a rough idea?

Thanks,
Peng.

> 
> 
> Juergen
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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Julien Grall]

On 27/11/2019 09:49, Peng Fan wrote:
>> Subject: Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER
>> range
>>
>> On 27.11.19 10:31, Peng Fan wrote:
>>>> Subject: Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix
>>>> GICD_ISACTIVER range
>>>>
>>>> On 27.11.19 01:01, Julien Grall wrote:
>>>>> Hi,
>>>>>
>>>>> On 26/11/2019 23:17, Stefano Stabellini wrote:
>>>>>> On Tue, 26 Nov 2019, Julien Grall wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> On 26/11/2019 20:43, Stefano Stabellini wrote:
>>>>>>>> + Juergen
>>>>>>>>
>>>>>>>> I missed that you weren't in CC to the original patch, sorry.
>>>>>>>> I think this patch should go in, as otherwise Linux 5.4 could run
>>>>>>>> into problems. It is also a pretty straightforward 4 lines patch.
>>>>>>>
>>>>>>> 5.5 (or 5.6) is not going to run on Xen for other reasons (still
>>>>>>> in the vGIC)... So I would not view this as critical.
>>>>>>
>>>>>> 5.5 is not out yet, in fact, the dev window has just opened. Isn't
>>>>>> your statement a bit premature?
>>>>>
>>>>> The GICv4.1 work [1] is going to prevent Linux booting on all
>>>>> current versions of Xen. While I can't confirm this is going to be
>>>>> merged in 5.5, I can tell you this will break.
>>>>>
>>>>>>
>>>>>> In any case, even if potential future Linux releases could have
>>>>>> other additional issues, I don't think it should change our current
>>>>>> view on this specific issue which affects 5.4, just released.
>>>>>
>>>>> The patch is definitely not as straightforward as you may think.
>>>>> Please refer to the discussion we had on the first version. I voiced
>>>>> concern about this approach and gave point what could go wrong with
>>>> happen.
>>>>>
>>>>> This patch may be better than the current state (i.e crashing), but
>>>>> this wasn't tested enough to confirm this is the correct things to
>>>>> do and no other bug will appear (I don't believe reading I*ACTIVER
>>>>> was ever tested before).
>>>>>
>>>>> It is an annoying bug, but this is only affecting 5.4 which has just
>>>>> been released. It feels to me this is a fairly risky choice to merge
>>>>> it qutie late in the release without a good graps of the problem (see
>> above).
>>>>>
>>>>> So I would definitly, prefer if this patch is getting through
>>>>> backport once we get more testing.
>>>>>
>>>>> We can still document the bug in the release note and point people
>>>>> to the patch.
>>>>>
>>>>> Anyway, this is Juergen choice here. But at least now he has the
>>>>> full picture...
>>>>>
>>>>> Cheers,
>>>>>
>>>>> [1]
>>>>>
>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flwn.
>>>>>
>>>>
>> net%2FArticles%2F800494%2F&data=02%7C01%7Cpeng.fan%40nxp.co
>>>> m%7Cdca
>>>>>
>>>>
>> dfb39240749ee675e08d772fcd3ba%7C686ea1d3bc2b4c6fa92cd99c5c30163
>>>> 5%7C0%7
>>>>>
>>>>
>> C0%7C637104302519996592&sdata=7Jv2IhI8HZgBTSuYzkEplFyhX1lzmv
>>>> d73xb5
>>>>> 2d6ERVQ%3D&reserved=0
>>>>>
>>>>
>>>> Thanks, Julien, for sharing your opinion.
>>>>
>>>> With that statement I'd like to defer this patch to 4.14.
>>>
>>> But without this patch, 5.4 kernel will crash. So you prefer we
>>> develop the solution as Julien suggested for 4.13?

Yes 5.4 will crash on Xen 4.13 (as any previous version of Xen). But I 
don't think this is right to push a patch late without a clear 
understanding of the problem.

The argument so far has been we already implemented I*ACTIVER like that 
so it is fine to continue like that. However, I am not convinced the 
path has ever been exercised with older release of Linux and 5.4 will 
work as intended on Xen 4.13 with this patch.

So I would recommend to read back my answer on v1 and trying to explain 
why this approach is acceptable to have.

>>
>> I certainly won't take a patch for 4.13 when a maintainer of the related code
>> has reservations against it.
>>
>> I think the best thing to do is to develop a proper patch the maintainers are
>> happy with and don't try to force it into 4.13 now.
>> Such a patch can still be backported to 4.13 later.
> 
> Ok.
> 
> Julien,
> 
> What's your suggestion to fix the issue? Do you have a rough idea?

You can have a look at what the new vGIC is doing (see 
vgic/vgic-mmio.c). I don't know how feasible it is with the current vGIC.

However, as I pointed out previously, this patch would be acceptable for 
the next version of Xen. But I don't think this is suitable for Xen 4.13 
because we don't have enough data to lower the risk of this patch.

Cheers,

-- 
Julien Grall

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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Stefano Stabellini]

[-- Attachment #1: Type: text/plain, Size: 5181 bytes --]

On Wed, 27 Nov 2019, Jürgen Groß wrote:
> On 27.11.19 10:31, Peng Fan wrote:
> > > Subject: Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER
> > > range
> > > 
> > > On 27.11.19 01:01, Julien Grall wrote:
> > > > Hi,
> > > > 
> > > > On 26/11/2019 23:17, Stefano Stabellini wrote:
> > > > > On Tue, 26 Nov 2019, Julien Grall wrote:
> > > > > > Hi,
> > > > > > 
> > > > > > On 26/11/2019 20:43, Stefano Stabellini wrote:
> > > > > > > + Juergen
> > > > > > > 
> > > > > > > I missed that you weren't in CC to the original patch, sorry.
> > > > > > > I think this patch should go in, as otherwise Linux 5.4 could run
> > > > > > > into problems. It is also a pretty straightforward 4 lines patch.
> > > > > > 
> > > > > > 5.5 (or 5.6) is not going to run on Xen for other reasons (still in
> > > > > > the vGIC)... So I would not view this as critical.
> > > > > 
> > > > > 5.5 is not out yet, in fact, the dev window has just opened. Isn't
> > > > > your statement a bit premature?
> > > > 
> > > > The GICv4.1 work [1] is going to prevent Linux booting on all current
> > > > versions of Xen. While I can't confirm this is going to be merged in
> > > > 5.5, I can tell you this will break.
> > > > 
> > > > > 
> > > > > In any case, even if potential future Linux releases could have other
> > > > > additional issues, I don't think it should change our current view on
> > > > > this specific issue which affects 5.4, just released.
> > > > 
> > > > The patch is definitely not as straightforward as you may think.
> > > > Please refer to the discussion we had on the first version. I voiced
> > > > concern about this approach and gave point what could go wrong with
> > > happen.
> > > > 
> > > > This patch may be better than the current state (i.e crashing), but
> > > > this wasn't tested enough to confirm this is the correct things to do
> > > > and no other bug will appear (I don't believe reading I*ACTIVER was
> > > > ever tested before).
> > > > 
> > > > It is an annoying bug, but this is only affecting 5.4 which has just
> > > > been released. It feels to me this is a fairly risky choice to merge
> > > > it qutie late in the release without a good graps of the problem (see
> > > > above).
> > > > 
> > > > So I would definitly, prefer if this patch is getting through backport
> > > > once we get more testing.
> > > > 
> > > > We can still document the bug in the release note and point people to
> > > > the patch.
> > > > 
> > > > Anyway, this is Juergen choice here. But at least now he has the full
> > > > picture...
> > > > 
> > > > Cheers,
> > > > 
> > > > [1]
> > > > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flwn.
> > > > 
> > > net%2FArticles%2F800494%2F&data=02%7C01%7Cpeng.fan%40nxp.co
> > > m%7Cdca
> > > > 
> > > dfb39240749ee675e08d772fcd3ba%7C686ea1d3bc2b4c6fa92cd99c5c30163
> > > 5%7C0%7
> > > > 
> > > C0%7C637104302519996592&sdata=7Jv2IhI8HZgBTSuYzkEplFyhX1lzmv
> > > d73xb5
> > > > 2d6ERVQ%3D&reserved=0
> > > > 
> > > 
> > > Thanks, Julien, for sharing your opinion.
> > > 
> > > With that statement I'd like to defer this patch to 4.14.
> > 
> > But without this patch, 5.4 kernel will crash. So you prefer
> > we develop the solution as Julien suggested for 4.13?
> 
> I certainly won't take a patch for 4.13 when a maintainer of the
> related code has reservations against it.
> 
> I think the best thing to do is to develop a proper patch the
> maintainers are happy with and don't try to force it into 4.13 now.
> Such a patch can still be backported to 4.13 later.

I chatted with Juergen and he explained to me something I didn't know
before. The release manager can only *block* a patch from being
committed, he/she cannot actually decide if the patch should be
committed or not for a given release. He/she cannot overrule a
maintainer either.

In this case, Juergen cannot make the decision on whether the patch
should go in 4.13 or not.

Although I couldn't reproduce the problem on Xilinx boards, I have to
take the community angle on this, and I would like to make sure our
releases work properly on any hardware, including NXP. Thus, I'll make
the case one more time, hoping that Julien might change his mind :-)

We know that the bug fix won't introduce any regressions because, as
Julien wrote, this code path was never used before. Also because of
that, waiting for the backport and more OSSTest runs won't make much of
a difference because OSSTest won't exercise this code path.

It is true that the original code handling GICD_ISACTIVER was never spec
compliant, and it should be fixed properly. However, that is not what
this patch addresses. That code, in addition from not being spec
compliant by design, it also happens to have a typo. Fixing the typo at
this stage of the release is appropriate at least to get a consistent
behavior in the handling of GICD_ISACTIVER*, and also for Linux 5.4 as
guest. Not to give a false impression to users, the warning ensures that
the underlying Xen behavior is flagged appropriately.

In short, I think the patch should go in now and there are no downsides
to it. That's it, I rest my case. Julien, I hope you'll reconsider.

[-- Attachment #2: Type: text/plain, Size: 157 bytes --]

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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Julien Grall]

Hi Stefano,

On 28/11/2019 01:12, Stefano Stabellini wrote:
> On Wed, 27 Nov 2019, Jürgen Groß wrote:
>> On 27.11.19 10:31, Peng Fan wrote:
>>>> Subject: Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER
>>>> range
>>>>
>>>> On 27.11.19 01:01, Julien Grall wrote:
>>>>> Hi,
>>>>>
>>>>> On 26/11/2019 23:17, Stefano Stabellini wrote:
>>>>>> On Tue, 26 Nov 2019, Julien Grall wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> On 26/11/2019 20:43, Stefano Stabellini wrote:
>>>>>>>> + Juergen
>>>>>>>>
>>>>>>>> I missed that you weren't in CC to the original patch, sorry.
>>>>>>>> I think this patch should go in, as otherwise Linux 5.4 could run
>>>>>>>> into problems. It is also a pretty straightforward 4 lines patch.
>>>>>>>
>>>>>>> 5.5 (or 5.6) is not going to run on Xen for other reasons (still in
>>>>>>> the vGIC)... So I would not view this as critical.
>>>>>>
>>>>>> 5.5 is not out yet, in fact, the dev window has just opened. Isn't
>>>>>> your statement a bit premature?
>>>>>
>>>>> The GICv4.1 work [1] is going to prevent Linux booting on all current
>>>>> versions of Xen. While I can't confirm this is going to be merged in
>>>>> 5.5, I can tell you this will break.
>>>>>
>>>>>>
>>>>>> In any case, even if potential future Linux releases could have other
>>>>>> additional issues, I don't think it should change our current view on
>>>>>> this specific issue which affects 5.4, just released.
>>>>>
>>>>> The patch is definitely not as straightforward as you may think.
>>>>> Please refer to the discussion we had on the first version. I voiced
>>>>> concern about this approach and gave point what could go wrong with
>>>> happen.
>>>>>
>>>>> This patch may be better than the current state (i.e crashing), but
>>>>> this wasn't tested enough to confirm this is the correct things to do
>>>>> and no other bug will appear (I don't believe reading I*ACTIVER was
>>>>> ever tested before).
>>>>>
>>>>> It is an annoying bug, but this is only affecting 5.4 which has just
>>>>> been released. It feels to me this is a fairly risky choice to merge
>>>>> it qutie late in the release without a good graps of the problem (see
>>>>> above).
>>>>>
>>>>> So I would definitly, prefer if this patch is getting through backport
>>>>> once we get more testing.
>>>>>
>>>>> We can still document the bug in the release note and point people to
>>>>> the patch.
>>>>>
>>>>> Anyway, this is Juergen choice here. But at least now he has the full
>>>>> picture...
>>>>>
>>>>> Cheers,
>>>>>
>>>>> [1]
>>>>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flwn.
>>>>>
>>>> net%2FArticles%2F800494%2F&data=02%7C01%7Cpeng.fan%40nxp.co
>>>> m%7Cdca
>>>>>
>>>> dfb39240749ee675e08d772fcd3ba%7C686ea1d3bc2b4c6fa92cd99c5c30163
>>>> 5%7C0%7
>>>>>
>>>> C0%7C637104302519996592&sdata=7Jv2IhI8HZgBTSuYzkEplFyhX1lzmv
>>>> d73xb5
>>>>> 2d6ERVQ%3D&reserved=0
>>>>>
>>>>
>>>> Thanks, Julien, for sharing your opinion.
>>>>
>>>> With that statement I'd like to defer this patch to 4.14.
>>>
>>> But without this patch, 5.4 kernel will crash. So you prefer
>>> we develop the solution as Julien suggested for 4.13?
>>
>> I certainly won't take a patch for 4.13 when a maintainer of the
>> related code has reservations against it.
>>
>> I think the best thing to do is to develop a proper patch the
>> maintainers are happy with and don't try to force it into 4.13 now.
>> Such a patch can still be backported to 4.13 later.
> 
> I chatted with Juergen and he explained to me something I didn't know
> before. The release manager can only *block* a patch from being
> committed, he/she cannot actually decide if the patch should be
> committed or not for a given release. He/she cannot overrule a
> maintainer either.
> 
> In this case, Juergen cannot make the decision on whether the patch
> should go in 4.13 or not.
> 
> Although I couldn't reproduce the problem on Xilinx boards, I have to
> take the community angle on this, and I would like to make sure our
> releases work properly on any hardware, including NXP. Thus, I'll make
> the case one more time, hoping that Julien might change his mind :-)

We had promise that patches to support NXP will be upstreamed, but this 
was never done. If you look at [1], there are a lot of patches on top of it.

So I don't think NXP boot out-of-box and therefore I don't think we 
should make the decision based on this.

> 
> We know that the bug fix won't introduce any regressions because, as
> Julien wrote, this code path was never used before. Also because of
> that, waiting for the backport and more OSSTest runs won't make much of
> a difference because OSSTest won't exercise this code path.

Conversely, we don't know how many regression this is going to be 
introducing for Linux 5.4 because this was only reproduced once and we 
know the implementation is incorrect.

But OSSTest is also testing different version of Linux and  5.4 should 
be tested soon (if not already), so we should also be able to exercise 
this code path.

> 
> It is true that the original code handling GICD_ISACTIVER was never spec
> compliant, and it should be fixed properly. However, that is not what
> this patch addresses. That code, in addition from not being spec
> compliant by design, it also happens to have a typo. Fixing the typo at
> this stage of the release is appropriate at least to get a consistent
> behavior in the handling of GICD_ISACTIVER*, and also for Linux 5.4 as
> guest. Not to give a false impression to users, the warning ensures that
> the underlying Xen behavior is flagged appropriately.

Again, you have no promise that this will make the right thing for Linux 
5.4.

This has been my point for the past week and ignored on the ground that 
some of the I*ACTIVER registers were implemented like that so we must 
continue to spread the false.

> 
> In short, I think the patch should go in now and there are no downsides
> to it. That's it, I rest my case. Julien, I hope you'll reconsider.
I don't really see the point to try to allow Linux 5.4 booting on Xen 
4.13 without knowing whether we are not going to uncovered more BUG 
around I*ACTIVER.

If you really want this patch in Xen 4.13, then you should read my mail 
on the first version and trying to answer me why this 5.4 is going to be 
safe running on Xen 4.13.

If you can't answer that, then there are no reason to get this patch Xen 
4.13.

I would have been happy to get this patch in next (not Xen 4.13), but 
this thread doesn't give me the confidence that someone sat done and 
fully understood the problem. So until someone is able to explain me 
whether this patch is safe:

NAcked-by: Julien Grall <julien@xen.org>

Cheers,

-- 
Julien Grall

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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Jürgen Groß]

On 28.11.19 09:14, Julien Grall wrote:
> Hi Stefano,
> 
> On 28/11/2019 01:12, Stefano Stabellini wrote:
>> On Wed, 27 Nov 2019, Jürgen Groß wrote:
>>> On 27.11.19 10:31, Peng Fan wrote:
>>>>> Subject: Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix 
>>>>> GICD_ISACTIVER
>>>>> range
>>>>>
>>>>> On 27.11.19 01:01, Julien Grall wrote:
>>>>>> Hi,
>>>>>>
>>>>>> On 26/11/2019 23:17, Stefano Stabellini wrote:
>>>>>>> On Tue, 26 Nov 2019, Julien Grall wrote:
>>>>>>>> Hi,
>>>>>>>>
>>>>>>>> On 26/11/2019 20:43, Stefano Stabellini wrote:
>>>>>>>>> + Juergen
>>>>>>>>>
>>>>>>>>> I missed that you weren't in CC to the original patch, sorry.
>>>>>>>>> I think this patch should go in, as otherwise Linux 5.4 could run
>>>>>>>>> into problems. It is also a pretty straightforward 4 lines patch.
>>>>>>>>
>>>>>>>> 5.5 (or 5.6) is not going to run on Xen for other reasons (still in
>>>>>>>> the vGIC)... So I would not view this as critical.
>>>>>>>
>>>>>>> 5.5 is not out yet, in fact, the dev window has just opened. Isn't
>>>>>>> your statement a bit premature?
>>>>>>
>>>>>> The GICv4.1 work [1] is going to prevent Linux booting on all current
>>>>>> versions of Xen. While I can't confirm this is going to be merged in
>>>>>> 5.5, I can tell you this will break.
>>>>>>
>>>>>>>
>>>>>>> In any case, even if potential future Linux releases could have 
>>>>>>> other
>>>>>>> additional issues, I don't think it should change our current 
>>>>>>> view on
>>>>>>> this specific issue which affects 5.4, just released.
>>>>>>
>>>>>> The patch is definitely not as straightforward as you may think.
>>>>>> Please refer to the discussion we had on the first version. I voiced
>>>>>> concern about this approach and gave point what could go wrong with
>>>>> happen.
>>>>>>
>>>>>> This patch may be better than the current state (i.e crashing), but
>>>>>> this wasn't tested enough to confirm this is the correct things to do
>>>>>> and no other bug will appear (I don't believe reading I*ACTIVER was
>>>>>> ever tested before).
>>>>>>
>>>>>> It is an annoying bug, but this is only affecting 5.4 which has just
>>>>>> been released. It feels to me this is a fairly risky choice to merge
>>>>>> it qutie late in the release without a good graps of the problem (see
>>>>>> above).
>>>>>>
>>>>>> So I would definitly, prefer if this patch is getting through 
>>>>>> backport
>>>>>> once we get more testing.
>>>>>>
>>>>>> We can still document the bug in the release note and point people to
>>>>>> the patch.
>>>>>>
>>>>>> Anyway, this is Juergen choice here. But at least now he has the full
>>>>>> picture...
>>>>>>
>>>>>> Cheers,
>>>>>>
>>>>>> [1]
>>>>>> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flwn. 
>>>>>>
>>>>>>
>>>>> net%2FArticles%2F800494%2F&data=02%7C01%7Cpeng.fan%40nxp.co
>>>>> m%7Cdca
>>>>>>
>>>>> dfb39240749ee675e08d772fcd3ba%7C686ea1d3bc2b4c6fa92cd99c5c30163
>>>>> 5%7C0%7
>>>>>>
>>>>> C0%7C637104302519996592&sdata=7Jv2IhI8HZgBTSuYzkEplFyhX1lzmv
>>>>> d73xb5
>>>>>> 2d6ERVQ%3D&reserved=0
>>>>>>
>>>>>
>>>>> Thanks, Julien, for sharing your opinion.
>>>>>
>>>>> With that statement I'd like to defer this patch to 4.14.
>>>>
>>>> But without this patch, 5.4 kernel will crash. So you prefer
>>>> we develop the solution as Julien suggested for 4.13?
>>>
>>> I certainly won't take a patch for 4.13 when a maintainer of the
>>> related code has reservations against it.
>>>
>>> I think the best thing to do is to develop a proper patch the
>>> maintainers are happy with and don't try to force it into 4.13 now.
>>> Such a patch can still be backported to 4.13 later.
>>
>> I chatted with Juergen and he explained to me something I didn't know
>> before. The release manager can only *block* a patch from being
>> committed, he/she cannot actually decide if the patch should be
>> committed or not for a given release. He/she cannot overrule a
>> maintainer either.
>>
>> In this case, Juergen cannot make the decision on whether the patch
>> should go in 4.13 or not.
>>
>> Although I couldn't reproduce the problem on Xilinx boards, I have to
>> take the community angle on this, and I would like to make sure our
>> releases work properly on any hardware, including NXP. Thus, I'll make
>> the case one more time, hoping that Julien might change his mind :-)
> 
> We had promise that patches to support NXP will be upstreamed, but this 
> was never done. If you look at [1], there are a lot of patches on top of 
> it.
> 
> So I don't think NXP boot out-of-box and therefore I don't think we 
> should make the decision based on this.
> 
>>
>> We know that the bug fix won't introduce any regressions because, as
>> Julien wrote, this code path was never used before. Also because of
>> that, waiting for the backport and more OSSTest runs won't make much of
>> a difference because OSSTest won't exercise this code path.
> 
> Conversely, we don't know how many regression this is going to be 
> introducing for Linux 5.4 because this was only reproduced once and we 
> know the implementation is incorrect.
> 
> But OSSTest is also testing different version of Linux and  5.4 should 
> be tested soon (if not already), so we should also be able to exercise 
> this code path.
> 
>>
>> It is true that the original code handling GICD_ISACTIVER was never spec
>> compliant, and it should be fixed properly. However, that is not what
>> this patch addresses. That code, in addition from not being spec
>> compliant by design, it also happens to have a typo. Fixing the typo at
>> this stage of the release is appropriate at least to get a consistent
>> behavior in the handling of GICD_ISACTIVER*, and also for Linux 5.4 as
>> guest. Not to give a false impression to users, the warning ensures that
>> the underlying Xen behavior is flagged appropriately.
> 
> Again, you have no promise that this will make the right thing for Linux 
> 5.4.
> 
> This has been my point for the past week and ignored on the ground that 
> some of the I*ACTIVER registers were implemented like that so we must 
> continue to spread the false.
> 
>>
>> In short, I think the patch should go in now and there are no downsides
>> to it. That's it, I rest my case. Julien, I hope you'll reconsider.
> I don't really see the point to try to allow Linux 5.4 booting on Xen 
> 4.13 without knowing whether we are not going to uncovered more BUG 
> around I*ACTIVER.

Sorry, but this is a rather weird statement.

IIUC you are saying that a typo blocking boot of Linux 5.4 should not be
fixed as you are not sure there are no other bugs?

> If you really want this patch in Xen 4.13, then you should read my mail 
> on the first version and trying to answer me why this 5.4 is going to be 
> safe running on Xen 4.13.

Or do you think that with the typo fixed and running Linux 5.4 guests
will destabilize the host?

If yes, what about meeting in the middle?

Add a Kconfig option to enable the typo fix and declare it as not
security supported when enabled. This will make it possible to evaluate
whether Linux 5.4 can be run on top of Xen without doing any harm.

> If you can't answer that, then there are no reason to get this patch Xen 
> 4.13.

For the initial 4.13 release it is too late anyway.

> I would have been happy to get this patch in next (not Xen 4.13), but 
> this thread doesn't give me the confidence that someone sat done and 
> fully understood the problem. So until someone is able to explain me 
> whether this patch is safe:
> 
> NAcked-by: Julien Grall <julien@xen.org>

Juergen

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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Julien Grall]

Hi,

On 28/11/2019 08:32, Jürgen Groß wrote:
> On 28.11.19 09:14, Julien Grall wrote:
>>> In short, I think the patch should go in now and there are no downsides
>>> to it. That's it, I rest my case. Julien, I hope you'll reconsider.
>> I don't really see the point to try to allow Linux 5.4 booting on Xen 
>> 4.13 without knowing whether we are not going to uncovered more BUG 
>> around I*ACTIVER.
> 
> Sorry, but this is a rather weird statement.
> 
> IIUC you are saying that a typo blocking boot of Linux 5.4 should not be
> fixed as you are not sure there are no other bugs?

The implementation of I*ACTIVER was incorrect but gone unnoticed because 
no-one used it until 5.4. It also happen that we didn't cover all the 
I*ACTIVER registers, so 5.4 crashes instead of using the wrong behavior.

This patch is basically replacing a guest crash by a behavior we don't 
fully understand.

> 
>> If you really want this patch in Xen 4.13, then you should read my 
>> mail on the first version and trying to answer me why this 5.4 is 
>> going to be safe running on Xen 4.13.
> 
> Or do you think that with the typo fixed and running Linux 5.4 guests
> will destabilize the host?

It is not going to destabilize the hosts. But this is not going to make 
5.4 running correctly as Xen guest.

Cheers,

-- 
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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Jürgen Groß]

On 28.11.19 09:48, Julien Grall wrote:
> Hi,
> 
> On 28/11/2019 08:32, Jürgen Groß wrote:
>> On 28.11.19 09:14, Julien Grall wrote:
>>>> In short, I think the patch should go in now and there are no downsides
>>>> to it. That's it, I rest my case. Julien, I hope you'll reconsider.
>>> I don't really see the point to try to allow Linux 5.4 booting on Xen 
>>> 4.13 without knowing whether we are not going to uncovered more BUG 
>>> around I*ACTIVER.
>>
>> Sorry, but this is a rather weird statement.
>>
>> IIUC you are saying that a typo blocking boot of Linux 5.4 should not be
>> fixed as you are not sure there are no other bugs?
> 
> The implementation of I*ACTIVER was incorrect but gone unnoticed because 
> no-one used it until 5.4. It also happen that we didn't cover all the 
> I*ACTIVER registers, so 5.4 crashes instead of using the wrong behavior.
> 
> This patch is basically replacing a guest crash by a behavior we don't 
> fully understand.
> 
>>
>>> If you really want this patch in Xen 4.13, then you should read my 
>>> mail on the first version and trying to answer me why this 5.4 is 
>>> going to be safe running on Xen 4.13.
>>
>> Or do you think that with the typo fixed and running Linux 5.4 guests
>> will destabilize the host?
> 
> It is not going to destabilize the hosts. But this is not going to make 
> 5.4 running correctly as Xen guest.

Have you verified it isn't running correctly or do you just think it
could hit problems?

In both cases I see no reason to keep wrong code.

Either the patch will let run Linux 5.4 fine - then the patch should
definitely be taken.

Or the patch will let Linux 5.4 boot further, but some problems will
occur. Then it will be possible to analyze those problems and try to
fix them, very possibly with the sane approach you are hoping for.


Juergen

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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Julien Grall]

On 28/11/2019 09:00, Jürgen Groß wrote:
> On 28.11.19 09:48, Julien Grall wrote:
>> Hi,
>>
>> On 28/11/2019 08:32, Jürgen Groß wrote:
>>> On 28.11.19 09:14, Julien Grall wrote:
>>>>> In short, I think the patch should go in now and there are no 
>>>>> downsides
>>>>> to it. That's it, I rest my case. Julien, I hope you'll reconsider.
>>>> I don't really see the point to try to allow Linux 5.4 booting on 
>>>> Xen 4.13 without knowing whether we are not going to uncovered more 
>>>> BUG around I*ACTIVER.
>>>
>>> Sorry, but this is a rather weird statement.
>>>
>>> IIUC you are saying that a typo blocking boot of Linux 5.4 should not be
>>> fixed as you are not sure there are no other bugs?
>>
>> The implementation of I*ACTIVER was incorrect but gone unnoticed 
>> because no-one used it until 5.4. It also happen that we didn't cover 
>> all the I*ACTIVER registers, so 5.4 crashes instead of using the wrong 
>> behavior.
>>
>> This patch is basically replacing a guest crash by a behavior we don't 
>> fully understand.
>>
>>>
>>>> If you really want this patch in Xen 4.13, then you should read my 
>>>> mail on the first version and trying to answer me why this 5.4 is 
>>>> going to be safe running on Xen 4.13.
>>>
>>> Or do you think that with the typo fixed and running Linux 5.4 guests
>>> will destabilize the host?
>>
>> It is not going to destabilize the hosts. But this is not going to 
>> make 5.4 running correctly as Xen guest.
> 
> Have you verified it isn't running correctly or do you just think it
> could hit problems?

I haven't tested myself, but any bug around vGIC is usually subtled. I 
wrote a long e-mail on v1 (see [1]) explaning what could happen.

To summarize briefly, Linux is reading the I*ACTIVER registers to check 
whether an interrupt is active at the hardware level. For instance, this 
is used to ensure all active interrupts have been handled before continuing.

By always returning 0, we tell Linux there are no interrupts. One of the 
risk is interrupts may be lost.

But that's Linux behavior, I can't tell how this is going to be used by 
others OSes.

> 
> In both cases I see no reason to keep wrong code.
> 
> Either the patch will let run Linux 5.4 fine - then the patch should
> definitely be taken.
That's up to Stefano and Peng to provide me information why this is 
fine. FAOD, the current justification provided is not acceptable for me.

> 
> Or the patch will let Linux 5.4 boot further, but some problems will
> occur. Then it will be possible to analyze those problems and try to
> fix them, very possibly with the sane approach you are hoping for.
> 
> 
> Juergen

[1] 
https://lore.kernel.org/xen-devel/7289f75f-1ab2-2d42-cd88-1be5306b3072@xen.org/

-- 
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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Stefano Stabellini]

On Thu, 28 Nov 2019, Julien Grall wrote:
> > In both cases I see no reason to keep wrong code.
> > 
> > Either the patch will let run Linux 5.4 fine - then the patch should
> > definitely be taken.
> That's up to Stefano and Peng to provide me information why this is fine.
> FAOD, the current justification provided is not acceptable for me.

I disagree. This is a typo fix. The original design was never spec
compliant. You cannot expect the typo fix to explain why the original
behavior is tolerable. That is out of scope and should *not* be required
for this fix.

We cannot expect typo fixes to go and trigger vgic/gic reworks and deep
investigations. This is a wrong expectation now, and going forward.

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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Julien Grall]

[-- Attachment #1.1: Type: text/plain, Size: 1278 bytes --]

On Thu, 28 Nov 2019, 18:09 Stefano Stabellini, <sstabellini@kernel.org>
wrote:

> On Thu, 28 Nov 2019, Julien Grall wrote:
> > > In both cases I see no reason to keep wrong code.
> > >
> > > Either the patch will let run Linux 5.4 fine - then the patch should
> > > definitely be taken.
> > That's up to Stefano and Peng to provide me information why this is fine.
> > FAOD, the current justification provided is not acceptable for me.
>
> I disagree. This is a typo fix. The original design was never spec
> compliant. You cannot expect the typo fix to explain why the original
> behavior is tolerable. That is out of scope and should *not* be required
> for this fix.


May I remind you that as a maintainer, this is in my right to say no to a
patch.


> We cannot expect typo fixes to go and trigger vgic/gic reworks and deep
> investigations. This is a wrong expectation now, and going forward.
>

That's the best way to turn Xen into a bunch of hacks.

I pointed out several times a potential issue with this patch. I also spent
some part of my week-end investigating it and provide some insight. Did you
look at them?

If you want this patch in, then please help explaining why 5.4 is going to
run fine on Xen 4.13 rather than keeping arguing this is a typo fix.

Cheers,

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[-- Attachment #2: Type: text/plain, Size: 157 bytes --]

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Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER range

[Peng Fan]

> Subject: Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix GICD_ISACTIVER
> range
> 
> Hi Stefano,
> 
> On 28/11/2019 01:12, Stefano Stabellini wrote:
> > On Wed, 27 Nov 2019, Jürgen Groß wrote:
> >> On 27.11.19 10:31, Peng Fan wrote:
> >>>> Subject: Re: [Xen-devel] [PATCH V2] arch: arm: vgic-v3: fix
> >>>> GICD_ISACTIVER range
> >>>>
> >>>> On 27.11.19 01:01, Julien Grall wrote:
> >>>>> Hi,
> >>>>>
> >>>>> On 26/11/2019 23:17, Stefano Stabellini wrote:
> >>>>>> On Tue, 26 Nov 2019, Julien Grall wrote:
> >>>>>>> Hi,
> >>>>>>>
> >>>>>>> On 26/11/2019 20:43, Stefano Stabellini wrote:
> >>>>>>>> + Juergen
> >>>>>>>>
> >>>>>>>> I missed that you weren't in CC to the original patch, sorry.
> >>>>>>>> I think this patch should go in, as otherwise Linux 5.4 could
> >>>>>>>> run into problems. It is also a pretty straightforward 4 lines patch.
> >>>>>>>
> >>>>>>> 5.5 (or 5.6) is not going to run on Xen for other reasons (still
> >>>>>>> in the vGIC)... So I would not view this as critical.
> >>>>>>
> >>>>>> 5.5 is not out yet, in fact, the dev window has just opened.
> >>>>>> Isn't your statement a bit premature?
> >>>>>
> >>>>> The GICv4.1 work [1] is going to prevent Linux booting on all
> >>>>> current versions of Xen. While I can't confirm this is going to be
> >>>>> merged in 5.5, I can tell you this will break.
> >>>>>
> >>>>>>
> >>>>>> In any case, even if potential future Linux releases could have
> >>>>>> other additional issues, I don't think it should change our
> >>>>>> current view on this specific issue which affects 5.4, just released.
> >>>>>
> >>>>> The patch is definitely not as straightforward as you may think.
> >>>>> Please refer to the discussion we had on the first version. I
> >>>>> voiced concern about this approach and gave point what could go
> >>>>> wrong with
> >>>> happen.
> >>>>>
> >>>>> This patch may be better than the current state (i.e crashing),
> >>>>> but this wasn't tested enough to confirm this is the correct
> >>>>> things to do and no other bug will appear (I don't believe reading
> >>>>> I*ACTIVER was ever tested before).
> >>>>>
> >>>>> It is an annoying bug, but this is only affecting 5.4 which has
> >>>>> just been released. It feels to me this is a fairly risky choice
> >>>>> to merge it qutie late in the release without a good graps of the
> >>>>> problem (see above).
> >>>>>
> >>>>> So I would definitly, prefer if this patch is getting through
> >>>>> backport once we get more testing.
> >>>>>
> >>>>> We can still document the bug in the release note and point people
> >>>>> to the patch.
> >>>>>
> >>>>> Anyway, this is Juergen choice here. But at least now he has the
> >>>>> full picture...
> >>>>>
> >>>>> Cheers,
> >>>>>
> >>>>> [1]
> >>>>>
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flwn.
> >>>>>
> >>>>
> net%2FArticles%2F800494%2F&data=02%7C01%7Cpeng.fan%40nxp.co
> >>>> m%7Cdca
> >>>>>
> >>>>
> dfb39240749ee675e08d772fcd3ba%7C686ea1d3bc2b4c6fa92cd99c5c30163
> >>>> 5%7C0%7
> >>>>>
> >>>>
> C0%7C637104302519996592&sdata=7Jv2IhI8HZgBTSuYzkEplFyhX1lzmv
> >>>> d73xb5
> >>>>> 2d6ERVQ%3D&reserved=0
> >>>>>
> >>>>
> >>>> Thanks, Julien, for sharing your opinion.
> >>>>
> >>>> With that statement I'd like to defer this patch to 4.14.
> >>>
> >>> But without this patch, 5.4 kernel will crash. So you prefer we
> >>> develop the solution as Julien suggested for 4.13?
> >>
> >> I certainly won't take a patch for 4.13 when a maintainer of the
> >> related code has reservations against it.
> >>
> >> I think the best thing to do is to develop a proper patch the
> >> maintainers are happy with and don't try to force it into 4.13 now.
> >> Such a patch can still be backported to 4.13 later.
> >
> > I chatted with Juergen and he explained to me something I didn't know
> > before. The release manager can only *block* a patch from being
> > committed, he/she cannot actually decide if the patch should be
> > committed or not for a given release. He/she cannot overrule a
> > maintainer either.
> >
> > In this case, Juergen cannot make the decision on whether the patch
> > should go in 4.13 or not.
> >
> > Although I couldn't reproduce the problem on Xilinx boards, I have to
> > take the community angle on this, and I would like to make sure our
> > releases work properly on any hardware, including NXP. Thus, I'll make
> > the case one more time, hoping that Julien might change his mind :-)
> 
> We had promise that patches to support NXP will be upstreamed, but this was
> never done. If you look at [1], there are a lot of patches on top of it.

That will happen after we rebase to 4.13. To support i.MX8 partition feature,
we introduced scfw api in XEN, this code might not be accepted by XEN
community, we have not find a good way for that.

Thanks,
Peng.

> 
> So I don't think NXP boot out-of-box and therefore I don't think we should
> make the decision based on this.

I not think this is only NXP issue although it only met by me currently.
It should be defer probe, but I have not look into the Linux code path.

Thanks,
Peng.

> 
> >
> > We know that the bug fix won't introduce any regressions because, as
> > Julien wrote, this code path was never used before. Also because of
> > that, waiting for the backport and more OSSTest runs won't make much
> > of a difference because OSSTest won't exercise this code path.
> 
> Conversely, we don't know how many regression this is going to be
> introducing for Linux 5.4 because this was only reproduced once and we know
> the implementation is incorrect.
> 
> But OSSTest is also testing different version of Linux and  5.4 should be
> tested soon (if not already), so we should also be able to exercise this code
> path.
> 
> >
> > It is true that the original code handling GICD_ISACTIVER was never
> > spec compliant, and it should be fixed properly. However, that is not
> > what this patch addresses. That code, in addition from not being spec
> > compliant by design, it also happens to have a typo. Fixing the typo
> > at this stage of the release is appropriate at least to get a
> > consistent behavior in the handling of GICD_ISACTIVER*, and also for
> > Linux 5.4 as guest. Not to give a false impression to users, the
> > warning ensures that the underlying Xen behavior is flagged appropriately.
> 
> Again, you have no promise that this will make the right thing for Linux 5.4.
> 
> This has been my point for the past week and ignored on the ground that
> some of the I*ACTIVER registers were implemented like that so we must
> continue to spread the false.
> 
> >
> > In short, I think the patch should go in now and there are no
> > downsides to it. That's it, I rest my case. Julien, I hope you'll reconsider.
> I don't really see the point to try to allow Linux 5.4 booting on Xen
> 4.13 without knowing whether we are not going to uncovered more BUG
> around I*ACTIVER.
> 
> If you really want this patch in Xen 4.13, then you should read my mail on the
> first version and trying to answer me why this 5.4 is going to be safe running
> on Xen 4.13.
> 
> If you can't answer that, then there are no reason to get this patch Xen 4.13.
> 
> I would have been happy to get this patch in next (not Xen 4.13), but this
> thread doesn't give me the confidence that someone sat done and fully
> understood the problem. So until someone is able to explain me whether this
> patch is safe:
> 
> NAcked-by: Julien Grall <julien@xen.org>
> 
> Cheers,
> 
> --
> Julien Grall
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