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Tue, 06 May 2025 03:43:46 -0700 (PDT) Date: Tue, 6 May 2025 12:43:45 +0200 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Julien Grall Cc: xen-devel@lists.xenproject.org, Anthony PERARD , Andrew Cooper , Michal Orzel , Jan Beulich , Stefano Stabellini , Juergen Gross , Christian Lindig , David Scott , Bertrand Marquis , Volodymyr Babchuk Subject: Re: [PATCH 8/9] xen: introduce flag when a domain requires cache control Message-ID: References: <20250506083148.34963-1-roger.pau@citrix.com> <20250506083148.34963-9-roger.pau@citrix.com> <035eeb54-e03b-463d-8ed8-b7041505322e@xen.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <035eeb54-e03b-463d-8ed8-b7041505322e@xen.org> On Tue, May 06, 2025 at 11:20:41AM +0100, Julien Grall wrote: > Hi Roger, > > On 06/05/2025 09:31, 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. > > Can you clarify whether you are talking about using the hypercall to flush > the cache or the instructions? On x86 at least: both hypercall and instructions if possible, since Xen traps cache flush instructions. Maybe that's different on ARM. As said on a previous reply I've assumed that cache_flush_permitted() was also relevant on ARM, but maybe it's not and domains are unconditionally allowed execution of cache control instructions and hypercalls. Thanks, Roger.