Re: [Qemu-devel] Dump guest page table inside QEMU makes system hang

[Blue Swirl]

On Tue, Aug 21, 2012 at 7:21 AM, 陳韋任 (Wei-Ren Chen)
<address@hidden> wrote:
> Hi all,
>
>   I want to dump guest page table when guest writes to cr3,
> the code snipt below,
>
> ---
> uint32_t pgd[1024][1024]; // guest page table
> static void dump_guest_pgtable(target_ulong cr3)
> {
>     int i, j;
>     uint32_t phyaddr = cr3;
>     uint32_t val;
>
>     for (i = 0; i < NUM_ENTRY; ++i)
>     {
>         phyaddr += i * 4;
>         for (j = 0; j < NUM_ENTRY; ++j)
>         {
>             cpu_physical_memory_read(phyaddr, &val, 4);
>             pgd[i][j] = val;
>         }
>     }
> }
>
> void cpu_x86_update_cr3(CPUX86State *env, target_ulong new_cr3)
> {
>     env->cr[3] = new_cr3; // guest cr3
>
>     if (env->cr[0] & CR0_PG_MASK) {
>         tlb_flush(env, 0);
>
>         // dump guest page table by using guest cr3
>         dump_guest_pgtable(new_cr3);
>     }
> }
> ---
>
>   The system will hang while booting. However, if I comment
> cpu_physical_memory_read in function dump_guest_pgtable, there
> is no problem. What I am missing here? Thanks.

cpu_physical_memory_read() can cause faults or other side effects like
MMIO. Using cpu_get_phys_page_debug() may help.

>
> Regards,
> chenwj
>
> --
> Wei-Ren Chen (陳韋任)
> Computer Systems Lab, Institute of Information Science,
> Academia Sinica, Taiwan (R.O.C.)
> Tel:886-2-2788-3799 #1667
> Homepage: http://people.cs.nctu.edu.tw/~chenwj
>