linux-kernel - Re: [PATCH] powerpc/64s: Clear PCR on boot

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Date:   Mon, 28 May 2018 23:28:34 +1000
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Guenter Roeck <linux@...ck-us.net>,
        Michael Ellerman <michael@...erman.id.au>
Cc:     Michael Neuling <mikey@...ling.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] powerpc/64s: Clear PCR on boot

On Sat, 2018-05-26 at 20:45 -0700, Guenter Roeck wrote:
> 
> I already have a patch, or at least one that does the trick for me.
> Getting qemu patched was not the problem. I just want to be sure that
> the problem is indeed a qemu problem.

Hey Guenter !

It's not quite the right patch though. The PCR is a hypervisor
priviledged register, your patch makes it supervisor accessible.

I don't have all my stuff at hand to provide a "proper" or tested patch
but it should look like

    spr_register_hv(env, SPR_PCR, "PCR",
                    SPR_NOACCESS, SPR_NOACCESS,
                    SPR_NOACCESS, SPR_NOACCESS,
                    &spr_read_generic, &spr_write_generic, 0);

Additionally the TCG ppc instruction decoder should be made to check
the PCR for varous instructions (that or use a specific write callback
that affects the CPU flags) but that's less urgent.

Cheers,
Ben.

> Thanks,
> Guenter
> 
> ---
> > From 1617bac264b4c49d817b6947611affa9b73318f6 Mon Sep 17 00:00:00 2001
> 
> From: Guenter Roeck <linux@...ck-us.net>
> Date: Fri, 25 May 2018 06:38:40 -0700
> Subject: [PATCH] PowerPC: Permit privileged access to SPR_PCR for POWER7+
> 
> Without this access, Linux mainline bails out.
> 
> Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> ---
>  target/ppc/translate_init.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/target/ppc/translate_init.c b/target/ppc/translate_init.c
> index 391b94b..3b09c49 100644
> --- a/target/ppc/translate_init.c
> +++ b/target/ppc/translate_init.c
> @@ -7953,11 +7953,12 @@ static void gen_spr_power6_common(CPUPPCState *env)
>  #endif
>      /*
>       * Register PCR to report POWERPC_EXCP_PRIV_REG instead of
> -     * POWERPC_EXCP_INVAL_SPR.
> +     * POWERPC_EXCP_INVAL_SPR in userspace. Permit privileged
> +     * access.
>       */
>      spr_register(env, SPR_PCR, "PCR",
>                   SPR_NOACCESS, SPR_NOACCESS,
> -                 SPR_NOACCESS, SPR_NOACCESS,
> +                 &spr_read_generic, &spr_write_generic,
>                   0x00000000);
>  }
>