Hi Ayan,
On 07/03/2024 12:39, Ayan Kumar Halder wrote:
From: Michal Orzel <michal.or...@amd.com>
Currently, if user enables HVC_DCC config option in Linux, it invokes access
to debug data transfer registers (i.e. DBGDTRTX_EL0 on arm64, DBGDTRTXINT on
arm32). As these registers are not emulated, Xen injects an undefined
exception to the guest and Linux crashes.
To prevent this crash, introduce a partial emulation of DBGDTR[TR]X_EL0
(these registers share the same encoding) as RAZ/WI and MDCCSR_EL0 as TXfull.
Refer ARM DDI 0487J.a ID042523, D19.3.8, DBGDTRTX_EL0
"If TXfull is set to 1, set DTRRX and DTRTX to UNKNOWN".
Thus, any OS is expected to read MDCCSR_EL0 and check for TXfull before
using DBGDTRTX_EL0. Linux does it via hvc_dcc_init() ---> hvc_dcc_check(),
and returns -ENODEV in case TXfull bit is still set after writing a test
character. This way we prevent the guest from making use of HVC DCC as a
console.
Signed-off-by: Michal Orzel <michal.or...@amd.com>
Signed-off-by: Ayan Kumar Halder <ayan.kumar.hal...@amd.com>
Acked-by: Julien Grall <jgr...@amazon.com>
Cheers,
--
Julien Grall
