[Xen-devel] [Xen-ARM: Linux] Grant table address, xen_hvm_resume_frames, is a phys_addr not a pfn

["Eric Trudeau" <etrudeau@xxxxxxxxxxxx>]

While working on our embedded ARM platform, we discovered a bug in the XEN
Linux ARM code where the grant table is being mapped into guest physical
memory at the wrong address because enlighten.c treats the
xen_hvm_resume_frames variable as if it was a pfn when, in fact, it is a 
physical
address.  Thus, instead of the address specified in the hypervisor node of the
device tree, e.g. 0xB0000000, the actual guest physical address is 0x000B0000.

Below is a _possible_ patch a developer from the Xen Linux team could try or
at least start from.  The kernel that we are using is based on an
older version, but I have made this suggested patch on recent linux-stable code.
It is not tested on the latest linux-stable code, but it has been tested on 
linux as
of commit bee980d9e9642e96351fa3ca9077b853ecf62f57.

Eric Trudeau
---
    XEN: Grant table address, xen_hvm_resume_frames, is a phys_addr not a pfn

    xen_hvm_resume_frames stores the physical address of the grant table.
    englighten.c was incorrectly setting it as if it was a page frame number.
    This caused the table to be mapped into the guest at an unexpected physical
    address.

    Additionally, a warning is improved to include the grant table address which
    failed in xen_remap.

    Signed-off-by: Eric Trudeau <etrudeau@xxxxxxxxxxxx>
---
 arch/arm/xen/enlighten.c  | 4 ++--
 drivers/xen/grant-table.c | 2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index 83e4f95..ceaf9d5 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -224,10 +224,10 @@ static int __init xen_guest_init(void)
        }
        if (of_address_to_resource(node, GRANT_TABLE_PHYSADDR, &res))
                return 0;
-       xen_hvm_resume_frames = res.start >> PAGE_SHIFT;
+       xen_hvm_resume_frames = res.start;
        xen_events_irq = irq_of_parse_and_map(node, 0);
        pr_info("Xen %s support found, events_irq=%d gnttab_frame_pfn=%lx\n",
-                       version, xen_events_irq, xen_hvm_resume_frames);
+                version, xen_events_irq, (xen_hvm_resume_frames >> 
PAGE_SHIFT));
        xen_domain_type = XEN_HVM_DOMAIN;

        xen_setup_features();
diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
index 62ccf54..0b4a741 100644
--- a/drivers/xen/grant-table.c
+++ b/drivers/xen/grant-table.c
@@ -1174,7 +1174,7 @@ static int gnttab_setup(void)
                gnttab_shared.addr = xen_remap(xen_hvm_resume_frames,
                                                PAGE_SIZE * max_nr_gframes);
                if (gnttab_shared.addr == NULL) {
-                       pr_warn("Failed to ioremap gnttab share frames!\n");
+                       pr_warn("Failed to ioremap gnttab share frames 
(addr=0x%08lx)!\n", xen_hvm_resume_frames);
                        return -ENOMEM;
                }
        }



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