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Date:   Fri, 17 Sep 2021 13:04:50 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@kernel.org>
To:     Jan Beulich <jbeulich@suse.com>
cc:     Juergen Gross <jgross@suse.com>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        lkml <linux-kernel@vger.kernel.org>,
        "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
        "hch@lst.de" <hch@lst.de>, Konrad Wilk <konrad.wilk@oracle.com>,
        "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>
Subject: Re: [PATCH v2 1/4] swiotlb-xen: ensure to issue well-formed
 XENMEM_exchange requests
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On Fri, 17 Sep 2021, Jan Beulich wrote:
> While the hypervisor hasn't been enforcing this, we would still better
> avoid issuing requests with GFNs not aligned to the requested order.
> Instead of altering the value also in the call to panic(), drop it
> there for being static and hence easy to determine without being part
> of the panic message.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>


> ---
> I question how useful it is to wrap "bytes" in PAGE_ALIGN(), when it is
> a multiple of a segment's size anyway (or at least was supposed to be,
> prior to "swiotlb-xen: maintain slab count properly"). But that's
> perhaps yet another separate patch.
> ---
> v2: Drop logging of alignment. Wrap lines.
> 
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -230,10 +230,11 @@ retry:
>  	/*
>  	 * Get IO TLB memory from any location.
>  	 */
> -	start = memblock_alloc(PAGE_ALIGN(bytes), PAGE_SIZE);
> +	start = memblock_alloc(PAGE_ALIGN(bytes),
> +			       IO_TLB_SEGSIZE << IO_TLB_SHIFT);
>  	if (!start)
> -		panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
> -		      __func__, PAGE_ALIGN(bytes), PAGE_SIZE);
> +		panic("%s: Failed to allocate %lu bytes\n",
> +		      __func__, PAGE_ALIGN(bytes));
>  
>  	/*
>  	 * And replace that memory with pages under 4GB.
>