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From: Thomas Monjalon <thomas@monjalon.net>
To: fengchengwen@huawei.com, Wenwu Ma <wenwux.ma@intel.com>
Cc: dev@dpdk.org, songx.jiale@intel.com, stable@dpdk.org
Subject: Re: [PATCH v3] dmadev: fix structure alignment
Date: Wed, 20 Mar 2024 12:37:16 +0100
Message-ID: <3047329.687JKscXgg@thomas>
In-Reply-To: <20240320072332.1433526-1-wenwux.ma@intel.com>
References: <20240308053711.1260154-1-wenwux.ma@intel.com>
<20240320072332.1433526-1-wenwux.ma@intel.com>
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Errors-To: stable-bounces@dpdk.org
20/03/2024 08:23, Wenwu Ma:
> The structure rte_dma_dev needs to be aligned to the cache line, but
> the return value of malloc may not be aligned to the cache line. When
> we use memset to clear the rte_dma_dev object, it may cause a segmentation
> fault in clang-x86-platform.
>
> This is because clang uses the "vmovaps" assembly instruction for
> memset, which requires that the operands (rte_dma_dev objects) must
> aligned on a 16-byte boundary or a general-protection exception (#GP)
> is generated.
>
> Therefore, either additional memory is applied for re-alignment, or the
> rte_dma_dev object does not require cache line alignment. The patch
> chooses the former option to fix the issue.
>
> Fixes: b36970f2e13e ("dmadev: introduce DMA device library")
> Cc: stable@dpdk.org
>
> Signed-off-by: Wenwu Ma <wenwux.ma@intel.com>
[..]
> - size = dma_devices_max * sizeof(struct rte_dma_dev);
> - rte_dma_devices = malloc(size);
> - if (rte_dma_devices == NULL)
> + /* The dma device object is expected to align cacheline, but
> + * the return value of malloc may not be aligned to the cache line.
> + * Therefore, extra memory is applied for realignment.
> + * note: We do not call posix_memalign/aligned_alloc because it is
> + * version dependent on libc.
> + */
> + size = dma_devices_max * sizeof(struct rte_dma_dev) +
> + RTE_CACHE_LINE_SIZE;
> + ptr = malloc(size);
> + if (ptr == NULL)
> return -ENOMEM;
> - memset(rte_dma_devices, 0, size);
> + memset(ptr, 0, size);
> +
> + rte_dma_devices = RTE_PTR_ALIGN(ptr, RTE_CACHE_LINE_SIZE);
Why not using aligned_alloc()?
https://en.cppreference.com/w/c/memory/aligned_alloc