[xen staging] x86/PV: make '0' debug key dump Dom0's stacks again

[patchbot@xxxxxxx]

commit 4843546fef5e024d5754f722fd01a8dfb482ac7d
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Oct 19 10:07:00 2021 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Oct 19 10:07:00 2021 +0200

    x86/PV: make '0' debug key dump Dom0's stacks again
    
    The conversion to __get_guest() failed to account for the fact that for
    remote vCPU-s dumping gets done through a pointer obtained from
    map_domain_page(): __get_guest() arranges for (apparent) accesses to
    hypervisor space to cause #GP(0).
    
    Fixes: 6a1d72d3739e ('x86: split __{get,put}_user() into "guest" and 
"unsafe" variants')
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/traps.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index 64f3396f20..4f3a7131d6 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -275,7 +275,9 @@ static void compat_show_guest_stack(struct vcpu *v,
     {
         if ( (((long)stack - 1) ^ ((long)(stack + 1) - 1)) & mask )
             break;
-        if ( __get_guest(addr, stack) )
+        if ( stack_page )
+            addr = *stack;
+        else if ( __get_guest(addr, stack) )
         {
             if ( i != 0 )
                 printk("\n    ");
@@ -344,7 +346,9 @@ static void show_guest_stack(struct vcpu *v, const struct 
cpu_user_regs *regs)
     {
         if ( (((long)stack - 1) ^ ((long)(stack + 1) - 1)) & mask )
             break;
-        if ( __get_guest(addr, stack) )
+        if ( stack_page )
+            addr = *stack;
+        else if ( __get_guest(addr, stack) )
         {
             if ( i != 0 )
                 printk("\n    ");
--
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