Messages in this thread | | | Date | Wed, 24 Jun 2015 15:11:24 -0500 | From | Timur Tabi <> | Subject | Re: [PATCH] ARM64: TTY: hvc_dcc: Add support for ARM64 dcc |
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On 06/22/2015 08:12 AM, Will Deacon wrote: > I still think we should be disabling userspace access to the DCC if the > kernel is using it as its console.
I still need help with this. I know you said a year ago that MDSCR_EL1.TDCC needs to be set to disable userspace access. Where and how should I do this? I can do this:
static int __init hvc_dcc_console_init(void) { #ifdef CONFIG_ARM64 u32 val;
asm("msr mdscr_el1, %0 " "orr %0, %0, #4096 " /* TDCC */ "msr %0, mdscr_el1 " : "=r" (val)); #endif
But this seems clunky.
I am concerned about KVM, though. There appears to be code in KVM in hyp.s and sys_regs.c that touches and/or emulates MDSCR_EL1.
On a side note, it does not appear that ARM32 blocks userspace DCC. I don't see where DBGDSCR.UDCCdis is set.
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