linux-kernel - Re: [PATCH 1/2] Revert "remoteproc: qcom_q6v5_mss: map/unmap metadata region before/after use"

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Message-ID: <20221223144731.GA4587@thinkpad>
Date:   Fri, 23 Dec 2022 20:17:31 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Uladzislau Rezki <urezki@...il.com>,
        linux-arm-msm@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        iommu@...ts.linux.dev
Subject: Re: [PATCH 1/2] Revert "remoteproc: qcom_q6v5_mss: map/unmap
 metadata region before/after use"

On Fri, Dec 23, 2022 at 10:27:02AM +0100, Christoph Hellwig wrote:
> This reverts commit fc156629b23a21181e473e60341e3a78af25a1d4.
> 
> This commit manages to do three API violations at once:
> 
>  - dereference the return value of dma_alloc_attrs with the
>    DMA_ATTR_NO_KERNEL_MAPPING mapping, which is clearly forbidden and
>    will do the wrong thing on various dma mapping implementations.  The
>    fact that dma-direct uses a struct page as a cookie is an undocumented
>    implementation detail
>  - include dma-map-ops.h and use pgprot_dmacoherent despite a clear
>    comment documenting that this is not acceptable
>  - use of the VM_DMA_COHERENT for something that is not the dma-mapping
>    code
>  - use of VM_FLUSH_RESET_PERMS for vmap, while it is only supported for
>    vmalloc
> 
> Signed-off-by: Christoph Hellwig <hch@....de>

Acked-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

Thanks,
Mani

> ---
>  drivers/remoteproc/qcom_q6v5_mss.c | 38 +++++-------------------------
>  1 file changed, 6 insertions(+), 32 deletions(-)
> 
> diff --git a/drivers/remoteproc/qcom_q6v5_mss.c b/drivers/remoteproc/qcom_q6v5_mss.c
> index fddb63cffee078..a8b141db4de63f 100644
> --- a/drivers/remoteproc/qcom_q6v5_mss.c
> +++ b/drivers/remoteproc/qcom_q6v5_mss.c
> @@ -10,7 +10,6 @@
>  #include <linux/clk.h>
>  #include <linux/delay.h>
>  #include <linux/devcoredump.h>
> -#include <linux/dma-map-ops.h>
>  #include <linux/dma-mapping.h>
>  #include <linux/interrupt.h>
>  #include <linux/kernel.h>
> @@ -933,52 +932,27 @@ static void q6v5proc_halt_axi_port(struct q6v5 *qproc,
>  static int q6v5_mpss_init_image(struct q6v5 *qproc, const struct firmware *fw,
>  				const char *fw_name)
>  {
> -	unsigned long dma_attrs = DMA_ATTR_FORCE_CONTIGUOUS | DMA_ATTR_NO_KERNEL_MAPPING;
> -	unsigned long flags = VM_DMA_COHERENT | VM_FLUSH_RESET_PERMS;
> -	struct page **pages;
> -	struct page *page;
> +	unsigned long dma_attrs = DMA_ATTR_FORCE_CONTIGUOUS;
>  	dma_addr_t phys;
>  	void *metadata;
>  	int mdata_perm;
>  	int xferop_ret;
>  	size_t size;
> -	void *vaddr;
> -	int count;
> +	void *ptr;
>  	int ret;
> -	int i;
>  
>  	metadata = qcom_mdt_read_metadata(fw, &size, fw_name, qproc->dev);
>  	if (IS_ERR(metadata))
>  		return PTR_ERR(metadata);
>  
> -	page = dma_alloc_attrs(qproc->dev, size, &phys, GFP_KERNEL, dma_attrs);
> -	if (!page) {
> +	ptr = dma_alloc_attrs(qproc->dev, size, &phys, GFP_KERNEL, dma_attrs);
> +	if (!ptr) {
>  		kfree(metadata);
>  		dev_err(qproc->dev, "failed to allocate mdt buffer\n");
>  		return -ENOMEM;
>  	}
>  
> -	count = PAGE_ALIGN(size) >> PAGE_SHIFT;
> -	pages = kmalloc_array(count, sizeof(struct page *), GFP_KERNEL);
> -	if (!pages) {
> -		ret = -ENOMEM;
> -		goto free_dma_attrs;
> -	}
> -
> -	for (i = 0; i < count; i++)
> -		pages[i] = nth_page(page, i);
> -
> -	vaddr = vmap(pages, count, flags, pgprot_dmacoherent(PAGE_KERNEL));
> -	kfree(pages);
> -	if (!vaddr) {
> -		dev_err(qproc->dev, "unable to map memory region: %pa+%zx\n", &phys, size);
> -		ret = -EBUSY;
> -		goto free_dma_attrs;
> -	}
> -
> -	memcpy(vaddr, metadata, size);
> -
> -	vunmap(vaddr);
> +	memcpy(ptr, metadata, size);
>  
>  	/* Hypervisor mapping to access metadata by modem */
>  	mdata_perm = BIT(QCOM_SCM_VMID_HLOS);
> @@ -1008,7 +982,7 @@ static int q6v5_mpss_init_image(struct q6v5 *qproc, const struct firmware *fw,
>  			 "mdt buffer not reclaimed system may become unstable\n");
>  
>  free_dma_attrs:
> -	dma_free_attrs(qproc->dev, size, page, phys, dma_attrs);
> +	dma_free_attrs(qproc->dev, size, ptr, phys, dma_attrs);
>  	kfree(metadata);
>  
>  	return ret < 0 ? ret : 0;
> -- 
> 2.35.1
> 

-- 
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