Hi Alexander, Thanks for your response, we are pursuing that option.
Based on this code<https://github.com/tianocore/edk2/blob/master/OvmfPkg/Library/PlatformInitLib/MemDetect.c#L562C1-L584C1> snippet, this -fw_cfg opt/ovmf/X-PciMmio64Mb is experimental, and we are not sure about the future support of this. Also, with this option we can only extend the MMIO up to 16TB not more than that. Hence wanted to see is there any other way we can increase the MMIO size. Thanks Ramkumar -----Original Message----- From: Alexander Gryanko <[email protected]> Sent: Thursday, August 20, 2026 3:24 PM To: [email protected]; Ramkumar Santhanakrishnan <[email protected]> Subject: Re: [edk2-devel] Regarding the dynamic MMIO window size !-------------------------------------------------------------------| CAUTION: External Email |-------------------------------------------------------------------! Hello Ramkumar, Have you tried changing the -fw_cfg opt/ovmf/X-PciMmio64Mb,string=XXXXX parameter? Doesn't that help? > On 20 Aug 2026, at 11:25, Ramkumar Santhanakrishnan via groups.io > <[email protected]<mailto:[email protected]>> > wrote: > > Hi > > I have a question about commit ecb778d0ac62560aa172786ba19521f27bc3f650, > which limits the MMIO window to 1/8 of the total physical address space. > For a guest with 46-bit physical addressing, this gives an 8 TB MMIO window. > We cannot increase the guest physical address width or move to 5-level paging > due to compatibility constraints. With newer GPUs (up to 512 GB VRAM each), 8 > TB may be insufficient for passthrough of 8 GPUs, mainly because each BAR > requires base address alignment. > We are evaluating increasing the MMIO window size. > Could you share the rationale for the 1/8 limit? > Do you see any concerns with changing it to 1/4, or making it configurable > from QEMU? > Thanks > Ramkumar > -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#122113): https://edk2.groups.io/g/devel/message/122113 Mute This Topic: https://groups.io/mt/120843033/21656 Group Owner: [email protected] Unsubscribe: https://edk2.groups.io/g/devel/unsub [[email protected]] -=-=-=-=-=-=-=-=-=-=-=-
