Re: [PATCH] KVM/arm: kernel low level debug support for ARM32 virtual platforms

[Will Deacon <will.deacon@arm.com>]

On Tue, Nov 03, 2015 at 09:44:52AM -0800, Mario Smarduch wrote:
> On 11/3/2015 8:33 AM, Christopher Covington wrote:
> > On 11/02/2015 06:51 PM, Mario Smarduch wrote:
> >>    this is a re-post from couple weeks ago, please take time to review this 
> >> simple patch which simplifies DEBUG_LL and prevents kernel crash on virtual 
> >> platforms.
> >>
> >> Before this patch DEBUG_LL for 'dummy virtual machine':
> >>
> >> ( ) Kernel low-level debugging via EmbeddedICE DCC channel
> >> ( ) Kernel low-level debug output via semihosting I/O
> >> ( ) Kernel low-level debugging via 8250 UART
> >> ( ) Kernel low-level debugging via ARM Ltd PL01x Primecell
> >>
> >> In summary if debug uart is not emulated kernel crashes.
> >> And once you pass that hurdle, uart physical/virtual addresses are unknown.
> >> DEBUG_LL comes in handy on many occasions and should be somewhat 
> >> intuitive to use like it is for physical platforms. For virtual platforms
> >> user may start daubting the host and get into a bigger mess.
> >>
> >> After this patch is applied user gets:
> >>
> >> (X) Kernel low-level debugging on QEMU Virtual Platform
> >> ( ) Kernel low-level debugging on Kvmtool Virtual Platform
> >> 	..... above repeated ....
> >>
> >> The virtual addresses selected follow arm reference models, high in vmalloc 
> >> section with high mem enabled and guest running with >= 1GB of memory. The 
> >> offset is leftover from arm reference models.
> > 
> > Which model? It doesn't appear to match the vexpress AEM/RTSM/FVP/whatever
> > which used 0x1c090000 for UART0.
> 
> I recall QEMU virt model had it's own physical address map, for sure I saw the
> virtio-mmio regions assigned in some ARM document. Peter would you know?
> 
> As far as kvmtool I'm not sure, currently PC1 COM1 port is used? Andre will that
> stay fixed?

We make absolutely no guarantees about the memory map provided by kvmtool.

Will