linux-kernel - RE: [PATCH rdma-next v1 1/1] RDMA/mana_ib: Fix bug in creation of dma regions

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Date: Thu, 8 Feb 2024 18:53:05 +0000
From: Konstantin Taranov <kotaranov@...rosoft.com>
To: Long Li <longli@...rosoft.com>, Konstantin Taranov
	<kotaranov@...ux.microsoft.com>, "sharmaajay@...rosoft.com"
	<sharmaajay@...rosoft.com>, "jgg@...pe.ca" <jgg@...pe.ca>, "leon@...nel.org"
	<leon@...nel.org>
CC: "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH rdma-next v1 1/1] RDMA/mana_ib: Fix bug in creation of dma
 regions

> From: Long Li <longli@...rosoft.com>
> Sent: Thursday, 8 February 2024 19:43
> To: Konstantin Taranov <kotaranov@...ux.microsoft.com>; Konstantin
> Taranov <kotaranov@...rosoft.com>; sharmaajay@...rosoft.com;
> jgg@...pe.ca; leon@...nel.org
> Cc: linux-rdma@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: RE: [PATCH rdma-next v1 1/1] RDMA/mana_ib: Fix bug in creation of
> dma regions
> 
> >
> >  	/* Hardware requires dma region to align to chosen page size */
> > -	page_sz = ib_umem_find_best_pgsz(umem, PAGE_SZ_BM, 0);
> > +	page_sz = ib_umem_find_best_pgsz(umem, PAGE_SZ_BM, virt);
> >  	if (!page_sz) {
> >  		ibdev_dbg(&dev->ib_dev, "failed to find page size.\n");
> >  		return -ENOMEM;
> >  	}
> 
> How about doing:
> page_sz = ib_umem_find_best_pgsz(umem, PAGE_SZ_BM, force_zero_offset
> ? 0 : virt);
> 
> Will this work? This can get rid of the following while loop.
> 

I do not think so. I mentioned once, that it was failing for me with existing code
with the 4K-aligned addresses and 8K pages. In this case, we miscalculate the 
number of pages. So, we think that it is one 8K page, but it is in fact two.


> > +
> > +	if (force_zero_offset) {
> > +		while (ib_umem_dma_offset(umem, page_sz) && page_sz >
> > PAGE_SIZE)
> > +			page_sz /= 2;
> > +		if (ib_umem_dma_offset(umem, page_sz) != 0) {
> > +			ibdev_dbg(&dev->ib_dev, "failed to find page size to
> > force zero offset.\n");
> > +			return -ENOMEM;
> > +		}
> > +	}
> > +