linux-kernel - Re: [PATCH 1/3] fixup mmu_features immediately after getting cpu pa features.

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Message-ID: <e67acb9b-dd8e-767a-b57b-f12b3b0fd44d@linux.ibm.com>
Date:   Mon, 4 Oct 2021 21:02:21 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Sourabh Jain <sourabhjain@...ux.ibm.com>, mpe@...erman.id.au
Cc:     hbathini@...ux.ibm.com, mahesh@...ux.vnet.ibm.com,
        linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
        Mahesh Salgaonkar <mahesh@...ux.ibm.com>,
        Abdul haleem <abdhalee@...ux.vnet.ibm.com>
Subject: Re: [PATCH 1/3] fixup mmu_features immediately after getting cpu pa
 features.

On 10/4/21 20:41, Sourabh Jain wrote:
> From: Mahesh Salgaonkar <mahesh@...ux.ibm.com>
> 
> On system with radix support available, early_radix_enabled() starts
> returning true for a small window (until mmu_early_init_devtree() is
> called) even when radix mode disabled on kernel command line. This causes
> ppc64_bolted_size() to return ULONG_MAX in HPT mode instead of supported
> segment size, during boot cpu paca allocation.
> 
> With kernel command line = "... disable_radix":
> 
> early_init_devtree:			  <- early_radix_enabled() = false
>    early_init_dt_scan_cpus:		  <- early_radix_enabled() = false
>        ...
>        check_cpu_pa_features:		  <- early_radix_enabled() = false
>        ...				^ <- early_radix_enabled() = TRUE
>        allocate_paca:			| <- early_radix_enabled() = TRUE
>            ...                           |
>            ppc64_bolted_size:		| <- early_radix_enabled() = TRUE
>                if (early_radix_enabled())| <- early_radix_enabled() = TRUE
>                    return ULONG_MAX;     |
>        ...                               |
>    ...					| <- early_radix_enabled() = TRUE
>    ...					| <- early_radix_enabled() = TRUE
>    mmu_early_init_devtree()              V
>    ...					  <- early_radix_enabled() = false
> 
> So far we have not seen any issue because allocate_paca() takes minimum of
> ppc64_bolted_size and rma_size while allocating paca. However it is better
> to close this window by fixing up the mmu features as early as possible.
> This fixes early_radix_enabled() and ppc64_bolted_size() to return valid
> values in radix disable mode. This patch will help subsequent patch to
> depend on early_radix_enabled() check while detecting supported segment
> size in HPT mode.
> 
> Signed-off-by: Mahesh Salgaonkar <mahesh@...ux.ibm.com>
> Signed-off-by: Sourabh Jain <sourabhjain@...ux.ibm.com>
> Reported-and-tested-by: Abdul haleem <abdhalee@...ux.vnet.ibm.com>
> ---
>   arch/powerpc/include/asm/book3s/64/mmu.h | 1 +
>   arch/powerpc/include/asm/mmu.h           | 1 +
>   arch/powerpc/kernel/prom.c               | 1 +
>   arch/powerpc/mm/init_64.c                | 5 ++++-
>   4 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
> index c02f42d1031e..69a89fa1330d 100644
> --- a/arch/powerpc/include/asm/book3s/64/mmu.h
> +++ b/arch/powerpc/include/asm/book3s/64/mmu.h
> @@ -197,6 +197,7 @@ extern int mmu_vmemmap_psize;
>   extern int mmu_io_psize;
>   
>   /* MMU initialization */
> +void mmu_cpu_feature_fixup(void);
>   void mmu_early_init_devtree(void);
>   void hash__early_init_devtree(void);
>   void radix__early_init_devtree(void);
> diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
> index 8abe8e42e045..c8eafd401fe9 100644
> --- a/arch/powerpc/include/asm/mmu.h
> +++ b/arch/powerpc/include/asm/mmu.h
> @@ -401,6 +401,7 @@ extern void early_init_mmu(void);
>   extern void early_init_mmu_secondary(void);
>   extern void setup_initial_memory_limit(phys_addr_t first_memblock_base,
>   				       phys_addr_t first_memblock_size);
> +static inline void mmu_cpu_feature_fixup(void) { }
>   static inline void mmu_early_init_devtree(void) { }
>   
>   static inline void pkey_early_init_devtree(void) {}
> diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
> index 2e67588f6f6e..1727a3abe6c1 100644
> --- a/arch/powerpc/kernel/prom.c
> +++ b/arch/powerpc/kernel/prom.c
> @@ -380,6 +380,7 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
>   		check_cpu_pa_features(node);
>   	}
>   
> +	mmu_cpu_feature_fixup();

can you do that call inside check_cpu_pa_features? or is it because we 
have the same issue with baremetal platforms?

Can we also rename this to indicate we are sanitizing the feature flag 
based on kernel command line.  Something like

/* Update cpu features based on kernel command line */
update_cpu_features();

>   	identical_pvr_fixup(node);
>   	init_mmu_slb_size(node);
>   
> diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
> index 386be136026e..9ed452605a2c 100644
> --- a/arch/powerpc/mm/init_64.c
> +++ b/arch/powerpc/mm/init_64.c
> @@ -437,12 +437,15 @@ static void __init early_check_vec5(void)
>   	}
>   }
>   
> -void __init mmu_early_init_devtree(void)
> +void __init mmu_cpu_feature_fixup(void)
>   {
>   	/* Disable radix mode based on kernel command line. */
>   	if (disable_radix)
>   		cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
> +}
>   
> +void __init mmu_early_init_devtree(void)
> +{
>   	/*
>   	 * Check /chosen/ibm,architecture-vec-5 if running as a guest.
>   	 * When running bare-metal, we can use radix if we like
>