Re:

[Julien Grall <julien@xxxxxxx>]

On 18/11/2022 07:47, Michal Orzel wrote:
> On 18/11/2022 03:00, Jiamei Xie wrote:
> > Date: Thu, 17 Nov 2022 11:07:12 +0800
> > Subject: [PATCH] xen/arm: vpl011: Make access to DMACR write-ignore
> >
> > When the guest kernel enables DMA engine with "CONFIG_DMA_ENGINE=y",
> > Linux SBSA PL011 driver will access PL011 DMACR register in some
> > functions. As chapter "B Generic UART" in "ARM Server Base System
> > Architecture"[1] documentation describes, SBSA UART doesn't support
> > DMA. In current code, when the kernel tries to access DMACR register,
> > Xen will inject a data abort:
> > Unhandled fault at 0xffffffc00944d048
> > Mem abort info:
> >    ESR = 0x96000000
> >    EC = 0x25: DABT (current EL), IL = 32 bits
> >    SET = 0, FnV = 0
> >    EA = 0, S1PTW = 0
> >    FSC = 0x00: ttbr address size fault
> > Data abort info:
> >    ISV = 0, ISS = 0x00000000
> >    CM = 0, WnR = 0
> > swapper pgtable: 4k pages, 39-bit VAs, pgdp=0000000020e2e000
> > [ffffffc00944d048] pgd=100000003ffff803, p4d=100000003ffff803, 
> > pud=100000003ffff803, pmd=100000003fffa803, pte=006800009c090f13
> > Internal error: ttbr address size fault: 96000000 [#1] PREEMPT SMP
> > ...
> > Call trace:
> >   pl011_stop_rx+0x70/0x80
> >   tty_port_shutdown+0x7c/0xb4
> >   tty_port_close+0x60/0xcc
> >   uart_close+0x34/0x8c
> >   tty_release+0x144/0x4c0
> >   __fput+0x78/0x220
> >   ____fput+0x1c/0x30
> >   task_work_run+0x88/0xc0
> >   do_notify_resume+0x8d0/0x123c
> >   el0_svc+0xa8/0xc0
> >   el0t_64_sync_handler+0xa4/0x130
> >   el0t_64_sync+0x1a0/0x1a4
> > Code: b9000083 b901f001 794038a0 8b000042 (b9000041)
> > ---[ end trace 83dd93df15c3216f ]---
> > note: bootlogd[132] exited with preempt_count 1
> > /etc/rcS.d/S07bootlogd: line 47: 132 Segmentation fault start-stop-daemon
> >
> > As discussed in [2], this commit makes the access to DMACR register
> > write-ignore as an improvement.
> As discussed earlier, if we decide to improve vpl011 (for now only Stefano 
> shared his opinion),
> then we need to mark *all* the PL011 registers that are not part of SBSA ar 
> RAZ/WI.
I would be fine to that. But I would like us to print a message using 
XENLOG_G_DEBUG to catch any OS that would touch those registers.
Cheers,

--
Julien Grall