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Date: Thu, 24 Apr 2025 11:07:44 +0300
From: Leon Romanovsky <leon@kernel.org>
To: Jason Gunthorpe <jgg@ziepe.ca>
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Subject: Re: [PATCH v9 10/24] mm/hmm: let users to tag specific PFN with DMA
 mapped bit
Message-ID: <20250424080744.GP48485@unreal>
References: <cover.1745394536.git.leon@kernel.org>
 <0a7c1e06269eee12ff8912fe0da4b7692081fcde.1745394536.git.leon@kernel.org>
 <7185c055-fc9e-4510-a9bf-6245673f2f92@redhat.com>
 <20250423181706.GT1213339@ziepe.ca>
 <36891b0e-d5fa-4cf8-a181-599a20af1da3@redhat.com>
 <20250423233335.GW1213339@ziepe.ca>
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In-Reply-To: <20250423233335.GW1213339@ziepe.ca>

On Wed, Apr 23, 2025 at 08:33:35PM -0300, Jason Gunthorpe wrote:
> On Wed, Apr 23, 2025 at 09:37:24PM +0300, Mika Penttilä wrote:
> > 
> > On 4/23/25 21:17, Jason Gunthorpe wrote:
> > > On Wed, Apr 23, 2025 at 08:54:05PM +0300, Mika Penttilä wrote:
> > >>> @@ -36,6 +38,13 @@ enum hmm_pfn_flags {
> > >>>  	HMM_PFN_VALID = 1UL << (BITS_PER_LONG - 1),
> > >>>  	HMM_PFN_WRITE = 1UL << (BITS_PER_LONG - 2),
> > >>>  	HMM_PFN_ERROR = 1UL << (BITS_PER_LONG - 3),
> > >>> +
> > >>> +	/*
> > >>> +	 * Sticky flags, carried from input to output,
> > >>> +	 * don't forget to update HMM_PFN_INOUT_FLAGS
> > >>> +	 */
> > >>> +	HMM_PFN_DMA_MAPPED = 1UL << (BITS_PER_LONG - 7),
> > >>> +
> > >> How is this playing together with the mapped order usage?
> > > Order shift starts at bit 8, DMA_MAPPED is at bit 7
> > 
> > hmm bits are the high bits, and order is 5 bits starting from
> > (BITS_PER_LONG - 8)
> 
> I see, so yes order occupies 5 bits [-4,-5,-6,-7,-8] and the
> DMA_MAPPED overlaps, it should be 9 not 7 because of the backwardness.

Thanks for the fix.