Re: [Qemu-devel] [PATCH] hw/mips: malta: Don't boot from flash with KVM T&E

[James Hogan <james.hogan@imgtec.com>]

On 20/06/14 14:17, Andreas Färber wrote:
> Hi,
> 
> Am 20.06.2014 13:47, schrieb James Hogan:
>> In KVM trap & emulate (T&E) mode the flash reset region at 0xbfc00000
>> isn't executable, which is why the minimal kernel bootloader is loaded
>> and executed from the last 1MB of DRAM instead.
>>
>> Therefore if no kernel is provided on the command line and KVM is
>> enabled, exit with an error since booting from flash will fail.
>>
>> Reported-by: Aurelien Jarno <aurelien@aurel32.net>
>> Signed-off-by: James Hogan <james.hogan@imgtec.com>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>>  hw/mips/mips_malta.c | 6 ++++++
>>  1 file changed, 6 insertions(+)
> 
> Previous commits have used just "mips_malta:", so suggest to do the same
> for consistency - or clean hw/mips/ dir up by renaming the file to just
> malta.c and use "mips/malta:".
> 
> http://git.qemu-project.org/?p=qemu.git;a=history;f=hw/mips/mips_malta.c;h=f4a7d47129526f6762eccc47251c8cf3cd27f928;hb=HEAD

Noted

> 
> That said,
> 
>> diff --git a/hw/mips/mips_malta.c b/hw/mips/mips_malta.c
>> index 8bc5392b4223..91b0ce566111 100644
>> --- a/hw/mips/mips_malta.c
>> +++ b/hw/mips/mips_malta.c
>> @@ -1052,6 +1052,12 @@ void mips_malta_init(MachineState *machine)
>>                               bootloader_run_addr, kernel_entry);
>>          }
>>      } else {
>> +        /* The flash region isn't executable from a KVM T&E guest */
>> +        if (kvm_enabled()) {
>> +            error_report("KVM enabled but no -kernel argument was specified. "
>> +                         "Booting from flash is not supported with KVM T&E.");
>> +            exit(1);
>> +        }
>>          /* Load firmware from flash. */
>>          if (!dinfo) {
>>              /* Load a BIOS image. */
> 
> Reviewed-by: Andreas Färber <afaerber@suse.de>
> 
> Are users expected to know/understand "KVM T&E"? You don't test for that
> T&E mode here, so you could either shorten the message to just "KVM" or
> replace the check with a more specific one.

Yeh, not mentioning T&E at all would be better actually. The limitation
is technically a MIPS KVM one rather than being T&E specific.

I'll post a v2.

Thanks for reviewing
James

> Since qtest does not use KVM on MIPS today, exiting without -kernel
> should be fine, but may need updating if we ever get to that.
> 
> Regards,
> Andreas
>