On Mon, May 12, 2025 at 05:24:01PM +0200, Jan Beulich wrote: > On 06.05.2025 10:31, Roger Pau Monne wrote: > > Such flag is added to the domain create hypercall, and a matching option is > > added to xl and libxl to set the flag: `cache_control`. When the flag is > > set, the domain is allowed the usage of cache control operations. If the > > flag is not explicitly set, libxl will set it if the domain has any `iomem` > > or `ioports` ranges assigned. > > > > Modify cache_flush_permitted() helper so that it's return value is no > > longer based on the IO resources assigned to the domain, but rather whether > > the domain has been explicitly allowed control over the cache, or if it has > > IOMMU support and there's a single IOMMU in the system that doesn't allow > > forcing snooping behind the guest back. As a result of this, the return of > > cache_flush_permitted() is constant for the lifetime of a domain, based on > > the domain creation flags and the capabilities of the IOMMU if enabled > > for the domain. > > This then further emphasizes the remark made for patch 7.
Hm, I think you are referring to the remark about how PCI device without IO resources would be handled then, and what would cache_flush_permitted() return then? IMO the benefit of the approach presented here is that it aims to know whether a domain needs cache control to be set at creation time, and not altered during it's runtime. Thanks, Roger.
