Re: [RFC PATCH v2 07/10] KVM: PPC: Ultravisor: Restrict LDBAR access

From: Paul Mackerras <paulus@ozlabs.org>
To: Claudio Carvalho <cclaudio@linux.ibm.com>
Cc: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>,
	Michael Anderson <andmike@linux.ibm.com>,
	Ram Pai <linuxram@us.ibm.com>,
	kvm-ppc@vger.kernel.org, Bharata B Rao <bharata@linux.ibm.com>,
	linuxppc-dev@ozlabs.org,
	Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>,
	Thiago Jung Bauermann <bauerman@linux.ibm.com>,
	Anshuman Khandual <khandual@linux.vnet.ibm.com>
Subject: Re: [RFC PATCH v2 07/10] KVM: PPC: Ultravisor: Restrict LDBAR access
Date: Mon, 20 May 2019 15:43:57 +1000	[thread overview]
Message-ID: <20190520054357.GB21382@blackberry> (raw)
In-Reply-To: <20190518142524.28528-8-cclaudio@linux.ibm.com>

On Sat, May 18, 2019 at 11:25:21AM -0300, Claudio Carvalho wrote:
> From: Ram Pai <linuxram@us.ibm.com>
> 
> When the ultravisor firmware is available, it takes control over the
> LDBAR register. In this case, thread-imc updates and save/restore
> operations on the LDBAR register are handled by ultravisor.
> 
> Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> [Restrict LDBAR access in assembly code and some in C, update the commit
>  message]
> Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com>

Some of the places that you are patching below are explicitly only
executed on POWER8, which can't have an ultravisor, and therefore
the change isn't needed:

> ---
>  arch/powerpc/kvm/book3s_hv.c                 |  4 +-
>  arch/powerpc/kvm/book3s_hv_rmhandlers.S      |  2 +
>  arch/powerpc/perf/imc-pmu.c                  | 64 ++++++++++++--------
>  arch/powerpc/platforms/powernv/idle.c        |  6 +-
>  arch/powerpc/platforms/powernv/subcore-asm.S |  4 ++
>  5 files changed, 52 insertions(+), 28 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 0fab0a201027..81f35f955d16 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -75,6 +75,7 @@
>  #include <asm/xics.h>
>  #include <asm/xive.h>
>  #include <asm/hw_breakpoint.h>
> +#include <asm/firmware.h>
>  
>  #include "book3s.h"
>  
> @@ -3117,7 +3118,8 @@ static noinline void kvmppc_run_core(struct kvmppc_vcore *vc)
>  			subcore_size = MAX_SMT_THREADS / split;
>  			split_info.rpr = mfspr(SPRN_RPR);
>  			split_info.pmmar = mfspr(SPRN_PMMAR);
> -			split_info.ldbar = mfspr(SPRN_LDBAR);
> +			if (!firmware_has_feature(FW_FEATURE_ULTRAVISOR))
> +				split_info.ldbar = mfspr(SPRN_LDBAR);

This is inside an if (is_power8) statement.

> diff --git a/arch/powerpc/platforms/powernv/subcore-asm.S b/arch/powerpc/platforms/powernv/subcore-asm.S
> index 39bb24aa8f34..e4383fa5e150 100644
> --- a/arch/powerpc/platforms/powernv/subcore-asm.S
> +++ b/arch/powerpc/platforms/powernv/subcore-asm.S
> @@ -44,7 +44,9 @@ _GLOBAL(split_core_secondary_loop)
>  
>  real_mode:
>  	/* Grab values from unsplit SPRs */
> +BEGIN_FW_FTR_SECTION
>  	mfspr	r6,  SPRN_LDBAR
> +END_FW_FTR_SECTION_IFCLR(FW_FEATURE_ULTRAVISOR)
>  	mfspr	r7,  SPRN_PMMAR
>  	mfspr	r8,  SPRN_PMCR
>  	mfspr	r9,  SPRN_RPR
> @@ -77,7 +79,9 @@ real_mode:
>  	mtspr	SPRN_HDEC, r4
>  
>  	/* Restore SPR values now we are split */
> +BEGIN_FW_FTR_SECTION
>  	mtspr	SPRN_LDBAR, r6
> +END_FW_FTR_SECTION_IFCLR(FW_FEATURE_ULTRAVISOR)

Only POWER8 supports split-core mode, so we can only get here on
POWER8.

Paul.