[Crash-utility] [PATCH v2] x86_64: Make the conversion between 4level and 5level paging automatically

[Dou Liyang]

Hi Dave,

At 07/11/2018 03:33 AM, Dave Anderson wrote:
> 
> The final phase of support would be making this work:
> 
>    static int
>    x86_64_task_uses_5level(struct task_context *tc)
>    {
>            return FALSE;
>    }
> 
> Have you had a chance to look at how that can be done?
> 

I have no idea to check if 5level paging is used in User-space.

You gave me some methods, and I have try:

   -The MAP_FIXED flag
   -check if the contents of the page directory or p4d is 'flods'

Now, I found a rough way. As We all know, in x86_64_uvtop_level4(),
the user virtual address is either 4-level or 5-level paging. Can we
do like that:

   if (machdep->flags & VM_5LEVEL)
       1) Using 5-level parsing code...
       2) Check if it is success
          If failed, Using 4-level parsing code...
   else
       Always using 4-level parsing code...

   3) go on...

Thanks,
	dou
--------------8<----------------

diff --git a/x86_64.c b/x86_64.c
index 07b6aa9..0e12825 100644
--- a/x86_64.c
+++ b/x86_64.c
@@ -1915,22 +1915,21 @@ x86_64_uvtop_level4(struct task_context *tc, 
ulong uvaddr, physaddr_t *paddr, in
                 goto no_upage;

         /* If the VM is in 5-level page table */
-       if (machdep->flags & VM_5LEVEL && x86_64_task_uses_5level(tc)) {
+       if (machdep->flags & VM_5LEVEL) {
                 ulong p4d_pte;
                 /*
                  *  p4d = p4d_offset(pgd, address);
                  */
                 p4d_pte = x86_64_p4d_offset(pgd_pte, uvaddr, verbose, 
FALSE);
-               if (!(p4d_pte & _PAGE_PRESENT))
-                       goto no_upage;
-               /*
-                *  pud = pud_offset(p4d, address);
-                */
-               pud_pte = x86_64_pud_offset(p4d_pte, uvaddr, verbose, 
FALSE);
+               if (!(p4d_pte & _PAGE_PRESENT)) {
+                       /* pud = pud_offset(pgd, address); */
+                       pud_pte = x86_64_pud_offset(pgd_pte, uvaddr, 
verbose, FALSE);
+               } else {
+                       /* pud = pud_offset(p4d, address); */
+                       pud_pte = x86_64_pud_offset(p4d_pte, uvaddr, 
verbose, FALSE);
+               }
         } else {
-               /*
-                *  pud = pud_offset(pgd, address);
-                */
+               /* pud = pud_offset(pgd, address); */
                 pud_pte = x86_64_pud_offset(pgd_pte, uvaddr, verbose, 
FALSE);
         }