On 14.11.2019 18:29, Durrant, Paul wrote: >> -----Original Message----- >> From: Xen-devel <xen-devel-boun...@lists.xenproject.org> On Behalf Of Jan >> Beulich >> Sent: 14 November 2019 16:42 >> To: xen-devel@lists.xenproject.org >> Cc: Juergen Gross <jgr...@suse.com>; Sander Eikelenboom >> <li...@eikelenboom.it>; Andrew Cooper <andrew.coop...@citrix.com> >> Subject: [Xen-devel] [PATCH v2 0/2] AMD/IOMMU: re-work mode updating >> >> update_paging_mode() in the AMD IOMMU code expects to be invoked with >> the PCI devices lock held. The check occurring only when the mode >> actually needs updating, the violation of this rule by the majority >> of callers did go unnoticed until per-domain IOMMU setup was changed >> to do away with on-demand creation of IOMMU page tables. > > Wouldn't it be safer to just get rid of update_paging_mode() and start > with a reasonable number of levels?
Andrew did basically ask the same, but I continue to be unconvinced: We can't pick a "reasonable" level, we have to pick the maximum a guest may end up using. Yet why would we want to have all guests pay the price of at least one unnecessary page walk level? I don't mean to say I'm entirely opposed, but trading code simplicity for performance is almost never an easy or obvious decision. Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
