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Re: Xen/ARM - Query about a data abort seen while reading GICD registers
- To: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>, Ayan Kumar Halder <ayan.kumar.halder@xxxxxxxxxx>
- From: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxxxxx>
- Date: Tue, 16 Nov 2021 16:24:58 +0000
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- Delivery-date: Tue, 16 Nov 2021 16:25:19 +0000
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Hi Bertrand,
Thanks for looking into it.
On 16/11/2021 15:36, Bertrand Marquis wrote:
Hi Ayan,
On 16 Nov 2021, at 15:27, Ayan Kumar Halder <ayan.kumar.halder@xxxxxxxxxx>
wrote:
Hi Xen/Arm experts,
I am facing a very strange issue while running a baremetal application as a
DomU guest on arm64 platform.
The baremetal app tries to read the GICD register with post indexing as follows
:-
ldr x1, =0x3001000
ldr w2, [x1], #4 <<<------ PC = 0x40000ca8
Increment on on load is not supported by the emulation layer.
That is surprising. The reason being if I try to read the GICC register
(0x3002000) with post indexing then it works fine.
Can you point me in source where this limitation is set ?
Could you try with:
add x1, x1, #4
ldr w2, [x1]
This worked fine.
-Ayan
Regards
Bertrand
And then I get :-
HSR=0x92000005 pc=0x00000040000ca8 gva=0x3001000 gpa=0x00000003001000
This problem occurs only while reading the GICD registers with post indexing.
If I read the register with pre-indexing, then I do not see any abort.
Alternatively, if I read GICC register with post indexing, I don't see the
abort either.
From the HSR value, I interpret it as
EC = 100100b # Data abort from lower exception
IL = 1b # 32 bit instruction trapped
DFSC = 101 # Translation fault level 1
On debugging, I found that the abort is triggered from
try_handle_mmio()
{ ...
/* All the instructions used on emulated MMIO region should be valid */
if ( !dabt.valid ) {
return IO_ABORT;
}
...
}
From the Arm V8 Arm specs, I understand that dabt.valid is ISV, bit[24] in "ISS
encoding for an exception from a Data Abort".
I saw that the caller is
do_trap_guest_sync() "case HSR_EC_DATA_ABORT_LOWER_EL"
where dabt.valid is false.
In the success scenario, dabt.valid is true.
I could not find the caller for do_trap_guest_sync()
So, can anyone help me here
1. Who is the caller for do_trap_guest_sync() ?
2. Any idea on what the issue is and how I can debug it further ?
Kind regards,
Ayan
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