Re: [PATCH v5.10.y] xen: replace xen_remap() with memremap()

[Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>]

On Tue, Sep 02, 2025 at 09:28:32AM +0000, Teddy Astie wrote:
> From: Juergen Gross <jgross@xxxxxxxx>
> 
> From: Juergen Gross <jgross@xxxxxxxx>
> 
> [ upstream commit 41925b105e345ebc84cedb64f59d20cb14a62613 ]
> 
> xen_remap() is used to establish mappings for frames not under direct
> control of the kernel: for Xenstore and console ring pages, and for
> grant pages of non-PV guests.
> 
> Today xen_remap() is defined to use ioremap() on x86 (doing uncached
> mappings), and ioremap_cache() on Arm (doing cached mappings).
> 
> Uncached mappings for those use cases are bad for performance, so they
> should be avoided if possible. As all use cases of xen_remap() don't
> require uncached mappings (the mapped area is always physical RAM),
> a mapping using the standard WB cache mode is fine.
> 
> As sparse is flagging some of the xen_remap() use cases to be not
> appropriate for iomem(), as the result is not annotated with the
> __iomem modifier, eliminate xen_remap() completely and replace all
> use cases with memremap() specifying the MEMREMAP_WB caching mode.
> 
> xen_unmap() can be replaced with memunmap().
> 
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Link: https://lore.kernel.org/r/20220530082634.6339-1-jgross@xxxxxxxx
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> Signed-off-by: Teddy Astie <teddy.astie@xxxxxxxxxx> [backport to 5.10.y]
> ---

Why is this needed for 5.10.y at all?  What bug does it fix?  And why
are you still using Xen on a 5.10.y kernel?  What prevents you from
moving to a newer one?

thanks,

greg k-h