[PATCH v3 3/9] powerpc: Introduce FW_FEATURE_ULTRAVISOR

Claudio Carvalho cclaudio at linux.ibm.com
Tue Jul 2 00:12:38 AEST 2019

On 6/15/19 4:36 AM, Paul Mackerras wrote:
> On Thu, Jun 06, 2019 at 02:36:08PM -0300, Claudio Carvalho wrote:
>> This feature tells if the ultravisor firmware is available to handle
>> ucalls.
> Everything in this patch that depends on CONFIG_PPC_UV should just
> depend on CONFIG_PPC_POWERNV instead.  The reason is that every host
> kernel needs to be able to do the ultracall to set partition table
> entry 0, in case it ends up being run on a machine with an ultravisor.
> Otherwise we will have the situation where a host kernel may crash
> early in boot just because the machine it's booted on happens to have
> an ultravisor running.  The crash will be a particularly nasty one
> because it will happen before we have probed the machine type and
> initialized the console; therefore it will just look like the machine
> hangs for no discernable reason.

> We also need to think about how to provide a way for petitboot to know
> whether the kernel it is booting knows how to do a ucall to set its
> partition table entry.  One suggestion would be to modify
> vmlinux.lds.S to add a new PT_NOTE entry in the program header of the
> binary with (say) a 64-bit doubleword which is a bitmap indicating
> capabilities of the binary.  We would define the first bit as
> indicating that the kernel knows how to run under an ultravisor.
> When running under an ultravisor, petitboot could then look for the
> PT_NOTE and the ultravisor-capable bit in it, and if the PT_NOTE is
> not there or the bit is zero, put up a dialog warning the user that
> the kernel will probably crash early in boot, and asking for explicit
> confirmation that the user wants to proceed.

I just posted a separated RFC patch for the ELF note.

Thanks, Claudio.

> Paul.

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