Re: [PATCH] xen/swiotlb: correct the check for xen_destroy_contiguous_region

From: JÃrgen GroÃ
Date: Tue Apr 28 2020 - 04:09:19 EST


On 28.04.20 09:33, peng.fan@xxxxxxx wrote:
From: Peng Fan <peng.fan@xxxxxxx>

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@xxxxxxx>
---
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);