Re: [PATCH v2 3/3] xen/swiotlb: remember having called xen_create_contiguous_region()

From: Juergen Gross <jgross@suse.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
	xen-devel <xen-devel@lists.xenproject.org>,
	Boris Ostrovsky <boris.ostrovsky@oracle.com>
Subject: Re: [PATCH v2 3/3] xen/swiotlb: remember having called xen_create_contiguous_region()
Date: Wed, 29 May 2019 12:21:41 +0200	[thread overview]
Message-ID: <55b35087-064d-8188-2373-0dd94ffef2b6__33117.8047157422$1559125358$gmane$org@suse.com> (raw)
In-Reply-To: <5CEE57910200007800233571@prv1-mh.provo.novell.com>

On 29/05/2019 11:57, Jan Beulich wrote:
>>>> On 29.05.19 at 11:04, <jgross@suse.com> wrote:
>> @@ -345,8 +346,11 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
>>  	size = 1UL << (order + XEN_PAGE_SHIFT);
>>  
>>  	if (!WARN_ON((dev_addr + size - 1 > dma_mask) ||
>> -		     range_straddles_page_boundary(phys, size)))
>> +		     range_straddles_page_boundary(phys, size)) &&
>> +	    PageXenRemapped(virt_to_page(vaddr))) {
>>  		xen_destroy_contiguous_region(phys, order);
>> +		ClearPageXenRemapped(virt_to_page(vaddr));
>> +	}
> 
> To be symmetric with setting the flag only after having made the region
> contiguous, and to avoid (perhaps just theoretical) races, wouldn't it be
> better to clear the flag before calling xen_destroy_contiguous_region()?
> Even better would be a TestAndClear...() operation.

I like that idea.

Juergen

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