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

[Yong LIU <yongliu@xxxxxxxxx>]

I use get_free_pages to get a contiguous virtual space, then get
physical address for DMA with virt_to_bus.
Regards
Yong. 
> Related to this, can you tell me whether the memory allocated to a domain is
> contiguous in machine RAM (given the calls to xen_create_contiguous, seems 
> like it is not)? 
> 
> Thanks,
> Himanshu
> 
> On Wed, Feb 15, 2006 at 02:13:52PM +0100, Mathieu Ropert wrote:
> > 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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