linux-kernel - Re: [PATCH] xen/swiotlb: correct the check for xen_destroy_contiguous

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Date:   Tue, 28 Apr 2020 10:09:08 +0200
From:   Jürgen Groß <jgross@...e.com>
To:     peng.fan@....com, konrad.wilk@...cle.com,
        boris.ostrovsky@...cle.com, sstabellini@...nel.org
Cc:     xen-devel@...ts.xenproject.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, linux-imx@....com
Subject: Re: [PATCH] xen/swiotlb: correct the check for
 xen_destroy_contiguous_region

On 28.04.20 09:33, peng.fan@....com wrote:
> From: Peng Fan <peng.fan@....com>
> 
> When booting xen on i.MX8QM, met:
> "
> [    3.602128] Unable to handle kernel paging request at virtual address 0000000000272d40
> [    3.610804] Mem abort info:
> [    3.613905]   ESR = 0x96000004
> [    3.617332]   EC = 0x25: DABT (current EL), IL = 32 bits
> [    3.623211]   SET = 0, FnV = 0
> [    3.626628]   EA = 0, S1PTW = 0
> [    3.630128] Data abort info:
> [    3.633362]   ISV = 0, ISS = 0x00000004
> [    3.637630]   CM = 0, WnR = 0
> [    3.640955] [0000000000272d40] user address but active_mm is swapper
> [    3.647983] Internal error: Oops: 96000004 [#1] PREEMPT SMP
> [    3.654137] Modules linked in:
> [    3.677285] Hardware name: Freescale i.MX8QM MEK (DT)
> [    3.677302] Workqueue: events deferred_probe_work_func
> [    3.684253] imx6q-pcie 5f000000.pcie: PCI host bridge to bus 0000:00
> [    3.688297] pstate: 60000005 (nZCv daif -PAN -UAO)
> [    3.688310] pc : xen_swiotlb_free_coherent+0x180/0x1c0
> [    3.693993] pci_bus 0000:00: root bus resource [bus 00-ff]
> [    3.701002] lr : xen_swiotlb_free_coherent+0x44/0x1c0
> "
> 
> In xen_swiotlb_alloc_coherent, if !(dev_addr + size - 1 <= dma_mask) or
> range_straddles_page_boundary(phys, size) are true, it will
> create contiguous region. So when free, we need to free contiguous
> region use upper check condition.

No, this will break PV guests on x86.

I think there is something wrong with your setup in combination with
the ARM xen_create_contiguous_region() implementation.

Stefano?


Juergen

> 
> Signed-off-by: Peng Fan <peng.fan@....com>
> ---
>   drivers/xen/swiotlb-xen.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index b6d27762c6f8..ab96e468584f 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -346,8 +346,8 @@ xen_swiotlb_free_coherent(struct device *hwdev, size_t size, void *vaddr,
>   	/* Convert the size to actually allocated. */
>   	size = 1UL << (order + XEN_PAGE_SHIFT);
>   
> -	if (!WARN_ON((dev_addr + size - 1 > dma_mask) ||
> -		     range_straddles_page_boundary(phys, size)) &&
> +	if (((dev_addr + size - 1 > dma_mask) ||
> +	    range_straddles_page_boundary(phys, size)) &&
>   	    TestClearPageXenRemapped(virt_to_page(vaddr)))
>   		xen_destroy_contiguous_region(phys, order);
>   
>