Re: [PATCH] drm/xe/pf: Keep VF LMEM BAR size low if no VFs enabled

["Bernatowicz, Marcin" <marcin.bernatowicz@linux.intel.com>]

On 9/18/2026 4:50 PM, Rodrigo Vivi wrote:
> On Fri, Sep 18, 2026 at 01:01:30PM +0200, Marcin Bernatowicz wrote:
>> When VFs are enabled on dGFX the driver resizes the PF VF_LMEM_BAR to
>> fit the requested layout. After VFs are disabled the PF VF BAR
>> size is left as-is. On platforms with tight MMIO apertures a
>> subsequent unplug/rescan followed by another enable may fail with:
>>
>>    "VF BAR …: can't assign; no space"
>>
>> because the PCI core reserves address space based on the (now large) VF
>> template, often multiplied by totalvfs.
>>
>> Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/5937
>> Fixes: 94eae6ee4c2d ("drm/xe/pf: Set VF LMEM BAR size")
>> Signed-off-by: Marcin Bernatowicz <marcin.bernatowicz@linux.intel.com>
>> Cc: Michał Wajdeczko <michal.wajdeczko@intel.com>
>> Cc: Michał Winiarski <michal.winiarski@intel.com>
>> ---
>> v4:
>>   - use directly pf_resize_vf_vram_bar helper with device_total_vfs value.
>> v3:
>>   - rebased to resolve conflicts, no other functional changes were done
>> v2:
>>   - Rename helper to restore_vf_vram_bar_size() (Michal)
>>   - Use xe->sriov.pf.device_total_vfs instead of pci_sriov_get_totalvfs(),
>>     which may be capped (Michal)
>>   - Switch logging to %pe (Michal)
>>   - Call restore unconditionally on enable-fail path (Michal)
>>     (drop vf_vram_bar_resized flag)
>> ---
>> ---
>>   drivers/gpu/drm/xe/xe_pci_sriov.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_pci_sriov.c b/drivers/gpu/drm/xe/xe_pci_sriov.c
>> index c023a2a1fc17..31abcee55211 100644
>> --- a/drivers/gpu/drm/xe/xe_pci_sriov.c
>> +++ b/drivers/gpu/drm/xe/xe_pci_sriov.c
>> @@ -177,6 +177,7 @@ static int pf_enable_vfs(struct xe_device *xe, int num_vfs)
>>   	return num_vfs;
>>   
>>   failed:
>> +	pf_resize_vf_vram_bar(xe, xe->sriov.pf.device_total_vfs);
> should we resize before unprovisioning?
> or it doesn't even matter at this point?!

The BAR size is independent of Xe/GuC provisioning, so resizing before 
unprovisioning is safe. It only requires SR-IOV memory decoding to be 
disabled.

>
>>   	xe_sriov_pf_unprovision_vfs(xe, num_vfs);
>>   	xe_pm_runtime_put(xe);
>>   	pf_finish_vfs_enabling(xe);
>> @@ -204,6 +205,8 @@ static int pf_disable_vfs(struct xe_device *xe)
>>   
>>   	pci_disable_sriov(pdev);
>>   
>> +	pf_resize_vf_vram_bar(xe, xe->sriov.pf.device_total_vfs);
> I just noticed that no users of this function handles the error.
> Should we convert it to void? (I see it already prints some messages,
> so not needed to duplicate anywhere)
>
> this is not a blocker and if the order above is okay:
The helper’s return type is unrelated to this fix, so I prefer to keep 
its interface unchanged here; it can be converted to void separately.
>
> Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

Thanks for the review.

marcin

>> +
>>   	xe_sriov_pf_reprovision_default(xe);
>>   
>>   	pf_reset_vfs(xe, num_vfs);
>> -- 
>> 2.43.0
>>