Re: [PATCH] powerpc: Fix up RTAS invocation for new qemu versions

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On Fri, Oct 04, 2019 at 01:54:35PM +0200, Paolo Bonzini wrote:
> On 04/10/19 12:38, David Gibson wrote:
> > In order to call RTAS functions on powerpc kvm-unit-tests relies on the
> > RTAS blob supplied by qemu.  But new versions of qemu don't supply an RTAS
> > blob: since the normal way for guests to get RTAS is to call the guest
> > firmware's instantiate-rtas function, we now rely on that guest firmware
> > to provide the RTAS code itself.
> > 
> > But qemu-kvm-tests bypasses the usual guest firmware to just run itself,
> > so we can't get the rtas blob from SLOF.
> > 
> > But.. in fact the RTAS blob under qemu is a bit of a sham anyway - it's
> > a tiny wrapper that forwards the RTAS call to a hypercall.  So, we can
> > just invoke that hypercall directly.
> > 
> > Signed-off-by: David Gibson <david@xxxxxxxxxxxxxxxxxxxxx>
> 
> Would it be hard to call instantiate-rtas?

Fairly.  First, we'd have to not use -bios to replace the normal SLOF
firmware - that could significantly slow down tests, since SLOF itself
takes a little while to start up.  Then we'd need to get the unit
tests to boot out of slof which is a different interface from the raw
one we're using now.  Then we'd need to get it to use the OF client
interface to call instantiate-rtas - we currently don't ever call OF
(obviously, since we don't even load it).

> I'm not sure if you have any
> interest in running kvm-unit-tests on hypervisors that might have a
> different way to process RTAS calls.

Probably not..?

> 
> Paolo
> 
> > ---
> >  lib/powerpc/asm/hcall.h |  3 +++
> >  lib/powerpc/rtas.c      |  6 +++---
> >  powerpc/cstart64.S      | 20 ++++++++++++++++----
> >  3 files changed, 22 insertions(+), 7 deletions(-)
> > 
> > So.. "new versions of qemu" in this case means ones that incorporate
> > the pull request I just sent today.
> > 
> > diff --git a/lib/powerpc/asm/hcall.h b/lib/powerpc/asm/hcall.h
> > index a8bd7e3..1173fea 100644
> > --- a/lib/powerpc/asm/hcall.h
> > +++ b/lib/powerpc/asm/hcall.h
> > @@ -24,6 +24,9 @@
> >  #define H_RANDOM		0x300
> >  #define H_SET_MODE		0x31C
> >  
> > +#define KVMPPC_HCALL_BASE	0xf000
> > +#define KVMPPC_H_RTAS		(KVMPPC_HCALL_BASE + 0x0)
> > +
> >  #ifndef __ASSEMBLY__
> >  /*
> >   * hcall_have_broken_sc1 checks if we're on a host with a broken sc1.
> > diff --git a/lib/powerpc/rtas.c b/lib/powerpc/rtas.c
> > index 2e7e0da..41c0a24 100644
> > --- a/lib/powerpc/rtas.c
> > +++ b/lib/powerpc/rtas.c
> > @@ -46,9 +46,9 @@ void rtas_init(void)
> >  	prop = fdt_get_property(dt_fdt(), node,
> >  				"linux,rtas-entry", &len);
> >  	if (!prop) {
> > -		printf("%s: /rtas/linux,rtas-entry: %s\n",
> > -				__func__, fdt_strerror(len));
> > -		abort();
> > +		/* We don't have a qemu provided RTAS blob, enter_rtas
> > +		 * will use H_RTAS directly */
> > +		return;
> >  	}
> >  	data = (u32 *)prop->data;
> >  	rtas_entry = (unsigned long)fdt32_to_cpu(*data);
> > diff --git a/powerpc/cstart64.S b/powerpc/cstart64.S
> > index ec673b3..972851f 100644
> > --- a/powerpc/cstart64.S
> > +++ b/powerpc/cstart64.S
> > @@ -121,13 +121,25 @@ halt:
> >  
> >  .globl enter_rtas
> >  enter_rtas:
> > +	LOAD_REG_ADDR(r11, rtas_entry)
> > +	ld	r10, 0(r11)
> > +
> > +	cmpdi	r10,0
> > +	bne	external_rtas
> > +
> > +	/* Use H_RTAS directly */
> > +	mr	r4,r3
> > +	lis	r3,KVMPPC_H_RTAS@h
> > +	ori	r3,r3,KVMPPC_H_RTAS@l
> > +	b	hcall
> > +
> > +external_rtas:
> > +	/* Use external RTAS blob */
> >  	mflr	r0
> >  	std	r0, 16(r1)
> >  
> > -	LOAD_REG_ADDR(r10, rtas_return_loc)
> > -	mtlr	r10
> > -	LOAD_REG_ADDR(r11, rtas_entry)
> > -	ld	r10, 0(r11)
> > +	LOAD_REG_ADDR(r11, rtas_return_loc)
> > +	mtlr	r11
> >  
> >  	mfmsr	r11
> >  	LOAD_REG_IMMEDIATE(r9, RTAS_MSR_MASK)
> > 
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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