[Xen-devel] Re: how to transfer virtual address into pyhsical address

[Mathieu Ropert <mro@xxxxxxxxxx>]

Yong LIU wrote:
> I write a very simple module to test memory address translation.
> When I install the module under xen 3.0, kernel panic. But when
> I install it under xen3.0 & kernel 2.6.16-rc2, it can work well.
>
> My question is: Is there a different way to translate virtual address
> into physical address under Xen 3.0?
> thanks for help. 
>
> dmesg information.
> --------------------------------------------------------
> hello: module license 'unspecified' taints kernel.
> Unable to handle kernel paging request at virtual address 3e0c5b0c
>  printing eip:
> f483c023
> *pde = ma 00000000 pa 55555000
> Oops: 0000 [#1]
> SMP
> Modules linked in: hello iptable_filter ip_tables video thermal
> processor fan button battery ac
> CPU:    1
> EIP:    0061:[<f483c023>]    Tainted: P      VLI
> EFLAGS: 00010206   (2.6.12.6-xen0-smp)
> EIP is at kvirt_to_pa+0x23/0x3c [hello]
> eax: 7e0c5000   ebx: f22c3000   ecx: 00000b0c   edx: 000003c8
> esi: f2026000   edi: c0000000   ebp: f2026000   esp: f2027f90
> ds: 007b   es: 007b   ss: 0069
> Process insmod (pid: 4710, threadinfo=f2026000 task=f27c4520)
> Stack: f483e01a f22c3000 f483c380 c013a1f8 c05a10a8 00000001 f483c380
> 0804a060
>        b7fb3ff4 b7fb5538 c0109021 0804a060 00000dda 0804a050 b7fb3ff4
> b7fb5538
>        bffd6558 00000080 0000007b c010007b 00000080 b7f5667e 00000073
> 00010246
> Call Trace:
>  [<f483e01a>] hello_init_module+0x1a/0x2d [hello]
>  [<c013a1f8>] sys_init_module+0x145/0x1e1
>  [<c0109021>] syscall_call+0x7/0xb
> Code:  Bad EIP value.
> -------------------------------------------------------
> here is the code.
> #include <linux/init.h>
> #include <linux/kernel.h>
> #include <linux/module.h>
>
> #include <asm/pgtable.h>
> #include <asm/page.h>
>
> static void kvirt_to_pa(void *vaddr)
> {
>         unsigned long addr=(unsigned long) vaddr;
>         unsigned long pte_value;
>         pgd_t *pgd=NULL;
>         pmd_t *pmd=NULL;
>         pte_t *pte=NULL;
>
>         pgd=pgd_offset_k(addr);
>         if(pgd_none(*pgd))
>                 goto hello_failed;
>         pmd=pmd_offset(pgd, addr);
>         if(pmd_none(*pmd))
>                 goto hello_failed;
>         pte=pte_offset_kernel(pmd, addr);
>         if(!pte_present(*pte))
>                 goto hello_failed;
>
>         pte_value= pte_val(*pte) & PAGE_MASK | (addr & (PAGE_SIZE - 1));
>         return;
>
> hello_failed:
>         printk(" failed\n");
>         return;
> }
> static int __init hello_init_module(void)
> {
>         void * page=NULL;
>         page=__get_free_pages(GFP_KERNEL, 0);
>         kvirt_to_pa(page);
>         free_page(page);
>         return 1;
> }
>
>
> static void __exit hello_exit_module(void)
> {
>         printk(" say bye\n");
>         return;
> }
> module_init(hello_init_module);
> module_exit(hello_exit_module);
__alloc_pages() returns a pointer to a page struct, not the virtual 
address of the allocated page. You can't use it directly like you do.
If you want the virtual address, either use page_address(page) or try 
some get_*_page function directly instead of alloc_pages().
Regards,
Mathieu

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