[PATCH] x86/pvshim: disable PDX compression in PV shim defconfig

[PATCH] x86/pvshim: disable PDX compression in PV shim defconfig

[Roger Pau Monne]

There's no need for PDX compression given the memory map provided by Xen
to guests is contiguous, turn off the feature by default in the PV shim
defconfig.

Reported-by: Jan Beulich <jbeulich@suse.com>
Fixes: c5c45bcbd6a1 ('pdx: introduce a new compression algorithm based on region offsets')
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
 xen/arch/x86/configs/pvshim_defconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/xen/arch/x86/configs/pvshim_defconfig b/xen/arch/x86/configs/pvshim_defconfig
index c58c29adb0bf..24f4e4857dde 100644
--- a/xen/arch/x86/configs/pvshim_defconfig
+++ b/xen/arch/x86/configs/pvshim_defconfig
@@ -7,6 +7,7 @@ CONFIG_PV_SHIM_EXCLUSIVE=y
 CONFIG_NR_CPUS=32
 CONFIG_EXPERT=y
 # Disable features not used by the PV shim
+CONFIG_PDX_NONE=y
 # CONFIG_XEN_SHSTK is not set
 # CONFIG_XEN_IBT is not set
 # CONFIG_GRANT_TABLE is not set
-- 
2.51.0

Re: [PATCH] x86/pvshim: disable PDX compression in PV shim defconfig

[Jan Beulich]

On 29.08.2025 09:51, Roger Pau Monne wrote:
> There's no need for PDX compression given the memory map provided by Xen
> to guests is contiguous, turn off the feature by default in the PV shim
> defconfig.
> 
> Reported-by: Jan Beulich <jbeulich@suse.com>
> Fixes: c5c45bcbd6a1 ('pdx: introduce a new compression algorithm based on region offsets')
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>

Acked-by: Jan Beulich <jbeulich@suse.com>

Not sure if a Fixes: tag is really appropriate here. The shim is working as
is, just carrying code which won't ever be used.

Jan

Re: [PATCH] x86/pvshim: disable PDX compression in PV shim defconfig

[Roger Pau Monné]

On Fri, Aug 29, 2025 at 10:10:59AM +0200, Jan Beulich wrote:
> On 29.08.2025 09:51, Roger Pau Monne wrote:
> > There's no need for PDX compression given the memory map provided by Xen
> > to guests is contiguous, turn off the feature by default in the PV shim
> > defconfig.
> > 
> > Reported-by: Jan Beulich <jbeulich@suse.com>
> > Fixes: c5c45bcbd6a1 ('pdx: introduce a new compression algorithm based on region offsets')
> > Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> 
> Acked-by: Jan Beulich <jbeulich@suse.com>
> 
> Not sure if a Fixes: tag is really appropriate here. The shim is working as
> is, just carrying code which won't ever be used.

I was borderline also, but I felt it was important to notice that the
change here should ideally had been part of that commit.  Do you have
a recommendation of any other tag I could use for that purpose?

Thanks, Roger.

Re: [PATCH] x86/pvshim: disable PDX compression in PV shim defconfig

[Jan Beulich]

On 29.08.2025 10:56, Roger Pau Monné wrote:
> On Fri, Aug 29, 2025 at 10:10:59AM +0200, Jan Beulich wrote:
>> On 29.08.2025 09:51, Roger Pau Monne wrote:
>>> There's no need for PDX compression given the memory map provided by Xen
>>> to guests is contiguous, turn off the feature by default in the PV shim
>>> defconfig.
>>>
>>> Reported-by: Jan Beulich <jbeulich@suse.com>
>>> Fixes: c5c45bcbd6a1 ('pdx: introduce a new compression algorithm based on region offsets')
>>> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
>>
>> Acked-by: Jan Beulich <jbeulich@suse.com>
>>
>> Not sure if a Fixes: tag is really appropriate here. The shim is working as
>> is, just carrying code which won't ever be used.
> 
> I was borderline also, but I felt it was important to notice that the
> change here should ideally had been part of that commit.  Do you have
> a recommendation of any other tag I could use for that purpose?

In rare cases I think I've used Amends: (not formally mentioned anywhere,
of course).

Jan

Re: [PATCH] x86/pvshim: disable PDX compression in PV shim defconfig

[Roger Pau Monné]

On Fri, Aug 29, 2025 at 12:21:26PM +0200, Jan Beulich wrote:
> On 29.08.2025 10:56, Roger Pau Monné wrote:
> > On Fri, Aug 29, 2025 at 10:10:59AM +0200, Jan Beulich wrote:
> >> On 29.08.2025 09:51, Roger Pau Monne wrote:
> >>> There's no need for PDX compression given the memory map provided by Xen
> >>> to guests is contiguous, turn off the feature by default in the PV shim
> >>> defconfig.
> >>>
> >>> Reported-by: Jan Beulich <jbeulich@suse.com>
> >>> Fixes: c5c45bcbd6a1 ('pdx: introduce a new compression algorithm based on region offsets')
> >>> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> >>
> >> Acked-by: Jan Beulich <jbeulich@suse.com>
> >>
> >> Not sure if a Fixes: tag is really appropriate here. The shim is working as
> >> is, just carrying code which won't ever be used.
> > 
> > I was borderline also, but I felt it was important to notice that the
> > change here should ideally had been part of that commit.  Do you have
> > a recommendation of any other tag I could use for that purpose?
> 
> In rare cases I think I've used Amends: (not formally mentioned anywhere,
> of course).

Oh, how would you feel about adding it formally to
sending-patches.pandoc?

It's a rare tag, but I would find it useful in contexts like the
above.

Thanks, Roger.