Le 02/09/2025 à 13:18, Greg Kroah-Hartman a écrit : > On Tue, Sep 02, 2025 at 09:28:32AM +0000, Teddy Astie wrote: >> From: Juergen Gross <[email protected]> >> >> From: Juergen Gross <[email protected]> >> >> [ 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 <[email protected]> >> Signed-off-by: Juergen Gross <[email protected]> >> Reviewed-by: Boris Ostrovsky <[email protected]> >> Acked-by: Stefano Stabellini <[email protected]> >> Link: https://lore.kernel.org/r/[email protected] >> Signed-off-by: Juergen Gross <[email protected]> >> Signed-off-by: Teddy Astie <[email protected]> [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? >
This patch is only useful for virtual machines (DomU) that runs this Linux version (a notable Linux distribution with this kernel branch is Debian 11); it's not useful for Dom0 kernels. On AMD platforms (and future Intel ones with TME); this patch along with [1] makes the caching attribute for access as WB instead of falling back to UC due to ioremap (within xen_remap) being used improving the performance as explained in the commit. [1] x86/hvmloader: select xen platform pci MMIO BAR UC or WB MTRR cache attribute https://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=22650d6054625be10172fe0c78b9cadd1a39bd63 > thanks, > > greg k-h > Teddy -- Teddy Astie | Vates XCP-ng Developer XCP-ng & Xen Orchestra - Vates solutions web: https://vates.tech
