linux-kernel - Re: [PATCH 4.9 12/16] net/rds: dma_map

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Date:   Fri, 3 Sep 2021 08:50:35 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Gerd Rausch <gerd.rausch@...cle.com>,
        Santosh Shilimkar <santosh.shilimkar@...cle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.9 12/16] net/rds: dma_map_sg is entitled to merge
 entries

Hi!

> [ Upstream commit fb4b1373dcab086d0619c29310f0466a0b2ceb8a ]
> 
> Function "dma_map_sg" is entitled to merge adjacent entries
> and return a value smaller than what was passed as "nents".
> 
> Subsequently "ib_map_mr_sg" needs to work with this value ("sg_dma_len")
> rather than the original "nents" parameter ("sg_len").
> 
> This old RDS bug was exposed and reliably causes kernel panics
> (using RDMA operations "rds-stress -D") on x86_64 starting with:
> commit c588072bba6b ("iommu/vt-d: Convert intel iommu driver to the iommu ops")
> 
> Simply put: Linux 5.11 and later.

I see this queued for 4.19 and 5.10 where "iommu/vt-d: Convert intel
iommu driver to the iommu ops" is not present. It may be okay for
older kernels, too, but I wanted to double-check.

Best regards,
								Pavel

> +++ b/net/rds/ib_frmr.c
> @@ -112,9 +112,9 @@ static int rds_ib_post_reg_frmr(struct rds_ib_mr *ibmr)
>  		cpu_relax();
>  	}
>  
> -	ret = ib_map_mr_sg_zbva(frmr->mr, ibmr->sg, ibmr->sg_len,
> +	ret = ib_map_mr_sg_zbva(frmr->mr, ibmr->sg, ibmr->sg_dma_len,
>  				&off, PAGE_SIZE);
> -	if (unlikely(ret != ibmr->sg_len))
> +	if (unlikely(ret != ibmr->sg_dma_len))
>  		return ret < 0 ? ret : -EINVAL;
>  
>  	/* Perform a WR for the fast_reg_mr. Each individual page

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