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Re: [PATCH] arm/arm64: xen: Fix to convert percpu address to gfn correctly

Hi Masami,

On 05/10/2020 14:39, Masami Hiramatsu wrote:
Use per_cpu_ptr_to_phys() instead of virt_to_phys() for per-cpu
address conversion.

In xen_starting_cpu(), per-cpu xen_vcpu_info address is converted
to gfn by virt_to_gfn() macro. However, since the virt_to_gfn(v)
assumes the given virtual address is in contiguous kernel memory
area, it can not convert the per-cpu memory if it is allocated on
vmalloc area (depends on CONFIG_SMP).

Are you sure about this? I have a .config with CONFIG_SMP=y where the per-cpu region for CPU0 is allocated outside of vmalloc area.

However, I was able to trigger the bug as soon as CONFIG_NUMA_BALANCING was enabled.


Fixes: 250c9af3d831 ("arm/xen: Add support for 64KB page granularity")

FWIW, I think the bug was already present before 250c9af3d831.

Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
  arch/arm/xen/enlighten.c |    2 +-
  include/xen/arm/page.h   |    3 +++
  2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
index e93145d72c26..a6ab3689b2f4 100644
--- a/arch/arm/xen/enlighten.c
+++ b/arch/arm/xen/enlighten.c
@@ -150,7 +150,7 @@ static int xen_starting_cpu(unsigned int cpu)
        pr_info("Xen: initializing cpu%d\n", cpu);
        vcpup = per_cpu_ptr(xen_vcpu_info, cpu);
- info.mfn = virt_to_gfn(vcpup);
+       info.mfn = percpu_to_gfn(vcpup);
        info.offset = xen_offset_in_page(vcpup);
err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info, xen_vcpu_nr(cpu),
diff --git a/include/xen/arm/page.h b/include/xen/arm/page.h
index 39df751d0dc4..ac1b65470563 100644
--- a/include/xen/arm/page.h
+++ b/include/xen/arm/page.h
@@ -83,6 +83,9 @@ static inline unsigned long bfn_to_pfn(unsigned long bfn)
  #define gfn_to_virt(m)                (__va(gfn_to_pfn(m) << XEN_PAGE_SHIFT))
+#define percpu_to_gfn(v) \
+       (pfn_to_gfn(per_cpu_ptr_to_phys(v) >> XEN_PAGE_SHIFT))
  /* Only used in PV code. But ARM guests are always HVM. */
  static inline xmaddr_t arbitrary_virt_to_machine(void *vaddr)


Julien Grall



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