linux-kernel - Re: [PATCH v2 4/4] CXL: Fix PSL error due to duplicate segment table entries

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Message-ID: <874muoy5ga.fsf@linux.vnet.ibm.com>
Date:	Tue, 28 Oct 2014 13:46:37 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Ian Munsie <imunsie@....ibm.com>, mpe <mpe@...erman.id.au>
Cc:	greg <greg@...ah.com>, arnd <arnd@...db.de>,
	benh <benh@...nel.crashing.org>, mikey <mikey@...ling.org>,
	anton <anton@...ba.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linuxppc-dev <linuxppc-dev@...abs.org>, jk <jk@...abs.org>,
	imunsie <imunsie@....ibm.com>,
	cbe-oss-dev <cbe-oss-dev@...ts.ozlabs.org>
Subject: Re: [PATCH v2 4/4] CXL: Fix PSL error due to duplicate segment table entries

Ian Munsie <imunsie@....ibm.com> writes:

> From: Ian Munsie <imunsie@....ibm.com>
>
> In certain circumstances the PSL (Power Service Layer, which provides
> translation services for CXL hardware) can send an interrupt for a
> segment miss that the kernel has already handled. This can happen if
> multiple translations for the same segment are queued in the PSL before
> the kernel has restarted the first translation.
>
> The CXL driver does not expect this situation and does not check if a
> segment had already been handled. This could cause a duplicate segment
> table entry which in turn caused a PSL error taking down the card.
>
> This patch fixes the issue by checking for existing entries in the
> segment table that match the segment it is trying to insert to avoid
> inserting duplicate entries.
>
> This patch requires "powerpc/copro: Use appropriate ESID mask in
> copro_calculate_slb" for the sste_matches function to operate correctly.
>
> Signed-off-by: Ian Munsie <imunsie@....ibm.com>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>

> ---
>  drivers/misc/cxl/fault.c | 28 ++++++++++++++++++++++------
>  1 file changed, 22 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/misc/cxl/fault.c b/drivers/misc/cxl/fault.c
> index cb4f323..c99e896 100644
> --- a/drivers/misc/cxl/fault.c
> +++ b/drivers/misc/cxl/fault.c
> @@ -21,11 +21,20 @@
>  
>  #include "cxl.h"
>  
> -/* This finds a free SSTE for the given SLB */
> +static bool sste_matches(struct cxl_sste *sste, struct copro_slb
> *slb)

inline ?

> +{
> +	return ((sste->vsid_data == cpu_to_be64(slb->vsid)) &&
> +		(sste->esid_data == cpu_to_be64(slb->esid)));

why comparing converting to big endian ? The natural way is to do it
other way right ?. 

          (be64_to_cpu(sste->vsid_data) == slb->vsid)

> +}
> +
> +/*
> + * This finds a free SSTE for the given SLB, or returns NULL if it's already in
> + * the segment table.
> + */
>  static struct cxl_sste* find_free_sste(struct cxl_context *ctx,
>  				       struct copro_slb *slb)
>  {
> -	struct cxl_sste *primary, *sste;
> +	struct cxl_sste *primary, *sste, *ret = NULL;
>  	unsigned int mask = (ctx->sst_size >> 7) - 1; /* SSTP0[SegTableSize] */
>  	unsigned int entry;
>  	unsigned int hash;
> @@ -38,15 +47,19 @@ static struct cxl_sste* find_free_sste(struct cxl_context *ctx,
>  	primary = ctx->sstp + (hash << 3);
>  
>  	for (entry = 0, sste = primary; entry < 8; entry++, sste++) {
> -		if (!(be64_to_cpu(sste->esid_data) & SLB_ESID_V))
> -			return sste;
> +		if (!ret && !(be64_to_cpu(sste->esid_data) & SLB_ESID_V))
> +			ret = sste;
> +		if (sste_matches(sste, slb))
> +			return NULL;
>  	}
> +	if (ret)
> +		return ret;
>  
>  	/* Nothing free, select an entry to cast out */
> -	sste = primary + ctx->sst_lru;
> +	ret = primary + ctx->sst_lru;
>  	ctx->sst_lru = (ctx->sst_lru + 1) & 0x7;
>  
> -	return sste;
> +	return ret;
>  }
>  
>  static void cxl_load_segment(struct cxl_context *ctx, struct copro_slb *slb)
> @@ -57,12 +70,15 @@ static void cxl_load_segment(struct cxl_context *ctx, struct copro_slb *slb)
>  
>  	spin_lock_irqsave(&ctx->sste_lock, flags);
>  	sste = find_free_sste(ctx, slb);
> +	if (!sste)
> +		goto out_unlock;
>  
>  	pr_devel("CXL Populating SST[%li]: %#llx %#llx\n",
>  			sste - ctx->sstp, slb->vsid, slb->esid);
>  
>  	sste->vsid_data = cpu_to_be64(slb->vsid);
>  	sste->esid_data = cpu_to_be64(slb->esid);
> +out_unlock:
>  	spin_unlock_irqrestore(&ctx->sste_lock, flags);
>  }
>  
> -- 
> 2.1.1
>
> --
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