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From:   Alistair Popple <apopple@nvidia.com>
To:     <akpm@linux-foundation.org>, <Felix.Kuehling@amd.com>,
        <linux-mm@kvack.org>, <rcampbell@nvidia.com>,
        <linux-ext4@vger.kernel.org>, <linux-xfs@vger.kernel.org>,
        Alex Sierra <alex.sierra@amd.com>
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        <hch@lst.de>, <jgg@nvidia.com>, <jglisse@redhat.com>,
        <willy@infradead.org>
Subject: Re: [PATCH v4 02/10] mm: add device coherent vma selection for memory migration
Date:   Fri, 28 Jan 2022 13:07:20 +1100
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On Thursday, 27 January 2022 2:09:41 PM AEDT Alex Sierra wrote:

[...]

> diff --git a/mm/migrate.c b/mm/migrate.c
> index 277562cd4cf5..2b3375e165b1 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -2340,8 +2340,6 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
>  			if (is_writable_device_private_entry(entry))
>  				mpfn |= MIGRATE_PFN_WRITE;
>  		} else {
> -			if (!(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
> -				goto next;

This isn't correct as it allows zero pfn pages to be selected for migration
when they shouldn't be (ie. because MIGRATE_VMA_SELECT_SYSTEM isn't specified).

>  			pfn = pte_pfn(pte);
>  			if (is_zero_pfn(pfn)) {
>  				mpfn = MIGRATE_PFN_MIGRATE;
> @@ -2349,6 +2347,13 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp,
>  				goto next;
>  			}
>  			page = vm_normal_page(migrate->vma, addr, pte);
> +			if (page && !is_zone_device_page(page) &&
> +			    !(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM))
> +				goto next;
> +			if (page && is_device_coherent_page(page) &&
> +			    (!(migrate->flags & MIGRATE_VMA_SELECT_DEVICE_COHERENT) ||
> +			     page->pgmap->owner != migrate->pgmap_owner))
> +				goto next;
>  			mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE;
>  			mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0;
>  		}
>