xen/arm: vpl011: emulate non-SBSA registers as WI/RAZ

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 non-SBSA registers
RAZ/WI as an improvement.

[1] https://developer.arm.com/documentation/den0094/c/?lang=en
[2] https://lore.kernel.org/xen-devel/alpine.DEB.2.22.394.2211161552420.4020@ubuntu-linux-20-04-desktop/

Signed-off-by: Jiamei Xie <jiamei.xie@arm.com>
Acked-by: Julien Grall <jgrall@amazon.com>
Reviewed-by: Michal Orzel <michal.orzel@amd.com>

diff --git a/xen/arch/arm/vpl011.c b/xen/arch/arm/vpl011.c
index f6144da1d7a0631125efc99e59a4c08c7a2133a0..c5b695469bc55901ff834bc2f935160544e2a067 100644 (file)
--- a/xen/arch/arm/vpl011.c
+++ b/xen/arch/arm/vpl011.c
@@ -403,11 +403,15 @@ static int vpl011_mmio_read(struct vcpu *v,
     default:
         gprintk(XENLOG_ERR, "vpl011: unhandled read r%d offset %#08x\n",
                 dabt.reg, vpl011_reg);
-        return 0;
+        goto read_as_zero;
     }
 
     return 1;
 
+read_as_zero:
+    *r = 0;
+    return 1;
+
 bad_width:
     gprintk(XENLOG_ERR, "vpl011: bad read width %d r%d offset %#08x\n",
             dabt.size, dabt.reg, vpl011_reg);
@@ -475,7 +479,7 @@ static int vpl011_mmio_write(struct vcpu *v,
     default:
         gprintk(XENLOG_ERR, "vpl011: unhandled write r%d offset %#08x\n",
                 dabt.reg, vpl011_reg);
-        return 0;
+        goto write_ignore;
     }
 
 write_ignore: