On Thu, 28 Jul 2022 15:17:49 +0800 Huang Rui <ray.hu...@amd.com> wrote:
> Hi Igor, > > Appreciate you for the reply! > > On Wed, Jul 27, 2022 at 04:19:30PM +0800, Igor Mammedov wrote: > > On Tue, 26 Jul 2022 15:27:07 +0800 > > Huang Rui <ray.hu...@amd.com> wrote: > > > > > Hi Anthony and other Qemu/Xen guys, > > > > > > We are trying to enable venus on Xen virtualization platform. And we would > > > like to use the backend memory with memory-backend-memfd,id=mem1,size=4G > > > options on QEMU, however, the QEMU will tell us the "-mem-path" is not > > > supported with Xen. I verified the same function on KVM. > > > > > > qemu-system-i386: -mem-path not supported with Xen > > > > > > So may I know whether Xen has any limitation that support > > > memory-backend-memfd in QEMU or just implementation is not done yet? > > > > Currently Xen doesn't use guest RAM allocation the way the rest of > > accelerators do. (it has hacks in memory_region/ramblock API, > > that divert RAM allocation calls to Xen specific API) > > I am new for Xen and QEMU, we are working on GPU. We would like to have a > piece of backend memroy like video memory for VirtIO GPU to support guest > VM Mesa Vulkan (Venus). Do you mean we can the memory_region/ramblock APIs > to work around it? > > > > > The sane way would extend Xen to accept RAM regions (whatever they are > > ram or fd based) QEMU allocates instead of going its own way. This way > > it could reuse all memory backends that QEMU provides for the rest of > > the non-Xen world. (not to mention that we could drop non trivial > > Xen hacks so that guest RAM handling would be consistent with other > > accelerators) > > > > May I know what do you mean by "going its own way"? This sounds good, could > you please elaborate on how can we implement this? We would like to give a > try to address the problem on Xen. Would you mind to point somewhere that I > can learn and understand the RAM region. Very happy to see your > suggestions! see for example see ram_block_add(), if Xen could be persuaded to use memory allocated by '!xen_enabled()' branch then it's likely file base backends would also become usable. Whether it is possible for Xen or not I don't know, I guess CCed Xen folks will suggest something useful. > Thanks & Best Regards, > Ray >
