[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 0/2] AMD/IOMMU: re-work mode updating
On 14.11.2019 18:29, Durrant, Paul wrote: >> -----Original Message----- >> From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of Jan >> Beulich >> Sent: 14 November 2019 16:42 >> To: xen-devel@xxxxxxxxxxxxxxxxxxxx >> Cc: Juergen Gross <jgross@xxxxxxxx>; Sander Eikelenboom >> <linux@xxxxxxxxxxxxxx>; Andrew Cooper <andrew.cooper3@xxxxxxxxxx> >> 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@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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