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Hello,

I’m trying to use vdispl interface from PV OS, it doesn’t work.
Configuration details:
    Xen 4.12.1
    Dom0: Linux 4.20.17-gentoo #13 SMP Sat Dec 28 11:12:24 MSK 2019 x86_64 Intel(R) Celeron(R) CPU N3050 @ 1.60GHz GenuineIntel GNU/Linux
    DomU: x86 Plan9, PV
    displ_be as a backend for vdispl and vkb

when VM starts, displ_be reports about an error:
gnttab: error: ioctl DMABUF_EXP_FROM_REFS failed: Invalid argument (displ_be.log:221)

related Dom0 output is:
[  191.579278] Cannot provide dma-buf: use_ptemode 1 (dmesg.create.log:123)

According to the linux kernel sources use_ptemod is:
gntdev.c:1213:  use_ptemod = !xen_feature(XENFEAT_auto_translated_physmap);

But xen-features.pl script doesn't show this feature is set for Dom0:
Xen features: 000028f0
enabled: pae_pgdir_above_4gb
enabled: mmu_pt_update_preserve_ad
enabled: dom0
enabled: memory_op_vnode_supported

According to the Xen sources, auto_translated_physmap is set up in a case of :
xen/common/kernel.c:467:            if ( paging_mode_translate(d) )
xen/common/kernel.c-468-                fi.submap |= 
xen/common/kernel.c-469-                    (1U << XENFEAT_writable_page_tables) |
xen/common/kernel.c-470-                    (1U << XENFEAT_auto_translated_physmap);

where
xen/include/asm-x86/paging.h:73:#define paging_mode_translate(_d) (!!((_d)->arch.paging.mode & PG_translate))

But PG_translate is applied only for HVM, at least I have not fount any other points:
xen/arch/x86/hvm/hvm.c:606:    rc = paging_enable(d, PG_refcounts|PG_translate|PG_external);

What should I do to make Xen set the feature up to continue using of vdispl?
And should I make any special support for the feature in PV OS?

All logs and configs are attached.

Thanks in advance.

Best regards,
    Alexander Sychev
[Xen-users] PV DRM doesn't work without auto_translated_physmap feature
