Re: [PATCH] scsi: ufs: core: Limit DMA alignment check

[Manivannan Sadhasivam <mani@kernel.org>]

On Wed, Feb 01, 2023 at 08:28:41AM -0800, Bjorn Andersson wrote:
> On Wed, Feb 01, 2023 at 03:57:48PM +0530, Manivannan Sadhasivam wrote:
> > On Tue, Jan 31, 2023 at 07:49:17PM -0800, Bjorn Andersson wrote:
> > > The three DMA memory regions allocated for the host memory space is
> > > documented to require alignment of 128, 1024 and 1024 respectively, but
> > > the returned address is checked for PAGE_SIZE alignment.
> > > 
> > > In the case these allocations are serviced by e.g. the Arm SMMU, the
> > > size and alignment will be determined by its supported page sizes. In
> > > most cases SZ_4K and a few larger sizes are available.
> > > 
> > > In the typical configuration this does not cause problems, but in the
> > > event that the system PAGE_SIZE is increased beyond 4k, it's no longer
> > > reasonable to expect that the allocation will be PAGE_SIZE aligned.
> > > 
> > > Limit the DMA alignment check to the actual alignment requirements
> > > written in the comments in the code, to avoid the UFS core refusing to
> > > initialize with such configuration.
> > 
> > Isn't dma_alloc_coherent() supposed to return PAGE_SIZE aligned dma and cpu
> > addresses? I suppose that could be reason for checking against PAGE_SIZE.
> > 
> 
> If the allocating device has associated dma_mem, the requested size will
> be rounded up to the next order and you will get an allocation which is
> sized and aligned to that.
> Given the three allocations on my device is 98304, 1024 and 640. The
> latter two would only be aligned to 1kb if this code path is taken...
> 
> 
> But in our case, the comment for __iommu_dma_alloc_noncontiguous() seems
> to give us the reason for the issue.
> 
> /*
>  * If size is less than PAGE_SIZE, then a full CPU page will be allocated,
>  * but an IOMMU which supports smaller pages might not map the whole thing.
>  */
> 

Ah, missed this part. Thanks for enlightening me :)

- Mani

> Our iommu reports supporting mapping of 4kb pages.
> 
> > > 
> > > Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
> > 
> > But it doesn't hurt to check for the actual alignment.
> > 
> > Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
> > 
> 
> Thanks,
> Bjorn
> 
> > Thanks,
> > Mani
> > 
> > > ---
> > >  drivers/ufs/core/ufshcd.c | 9 +++------
> > >  1 file changed, 3 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> > > index ec732e4bbbf4..d7f3f1ba9d12 100644
> > > --- a/drivers/ufs/core/ufshcd.c
> > > +++ b/drivers/ufs/core/ufshcd.c
> > > @@ -3724,12 +3724,9 @@ static int ufshcd_memory_alloc(struct ufs_hba *hba)
> > >  
> > >  	/*
> > >  	 * UFSHCI requires UTP command descriptor to be 128 byte aligned.
> > > -	 * make sure hba->ucdl_dma_addr is aligned to PAGE_SIZE
> > > -	 * if hba->ucdl_dma_addr is aligned to PAGE_SIZE, then it will
> > > -	 * be aligned to 128 bytes as well
> > >  	 */
> > >  	if (!hba->ucdl_base_addr ||
> > > -	    WARN_ON(hba->ucdl_dma_addr & (PAGE_SIZE - 1))) {
> > > +	    WARN_ON(hba->ucdl_dma_addr & (128 - 1))) {
> > >  		dev_err(hba->dev,
> > >  			"Command Descriptor Memory allocation failed\n");
> > >  		goto out;
> > > @@ -3745,7 +3742,7 @@ static int ufshcd_memory_alloc(struct ufs_hba *hba)
> > >  						   &hba->utrdl_dma_addr,
> > >  						   GFP_KERNEL);
> > >  	if (!hba->utrdl_base_addr ||
> > > -	    WARN_ON(hba->utrdl_dma_addr & (PAGE_SIZE - 1))) {
> > > +	    WARN_ON(hba->utrdl_dma_addr & (1024 - 1))) {
> > >  		dev_err(hba->dev,
> > >  			"Transfer Descriptor Memory allocation failed\n");
> > >  		goto out;
> > > @@ -3769,7 +3766,7 @@ static int ufshcd_memory_alloc(struct ufs_hba *hba)
> > >  						    &hba->utmrdl_dma_addr,
> > >  						    GFP_KERNEL);
> > >  	if (!hba->utmrdl_base_addr ||
> > > -	    WARN_ON(hba->utmrdl_dma_addr & (PAGE_SIZE - 1))) {
> > > +	    WARN_ON(hba->utmrdl_dma_addr & (1024 - 1))) {
> > >  		dev_err(hba->dev,
> > >  		"Task Management Descriptor Memory allocation failed\n");
> > >  		goto out;
> > > -- 
> > > 2.25.1
> > > 
> > 
> > -- 
> > மணிவண்ணன் சதாசிவம்

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