Re: [Xen-devel] Re: Linux Stubdom Problem

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 14 Sep 2011, Jiageng Yu wrote:
> Hi Stefano,
> 
>      I just have a prototype of vram mapping and test it now. The
> implementation of linux-stubdom kernel part is as follows.
> xen_remap_domain_mfn_range2 function maps foreign dom's physical
> address into linux kernel space. It is similar to
> xen_remap_domain_mfn_range. But xen_remap_domain_mfn_range is used to
> map foreign pages into linux user space.
> 
>     But the page info seems wrong after executing xen_remap_domain_mfn_range2.
> 
>     struct page *page=pfn_to_page(vmalloc_to_pfn(info->fb));
> 
>     The page->_count = 0xc2c2c2c2. It is very strange.
> 
>     Did I do the right thing?
> 

use page_address instead of pfn_to_page to find the struct page


>     Greeting.
> 
> Jiageng Yu.
> 
> 
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index 204e3ba..72a7808 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -2693,6 +2693,73 @@ out:
>  }
>  EXPORT_SYMBOL_GPL(xen_remap_domain_mfn_range);
> 
> +int xen_remap_domain_mfn_range2(unsigned long addr,unsigned long gpfn,
> +                int nr, unsigned domid)
> +{
> +    struct remap_data rmd;
> +    struct mmu_update mmu_update[REMAP_BATCH_SIZE];
> +    int level,i,batch,nr_page = nr;
> +    unsigned long range;
> +    int err = 0;
> +    unsigned long vaddr,base_addr = addr;
> +    pte_t pte,*ptep;
> +
> +    rmd.mfn = gpfn;
> +    rmd.prot = __pgprot(_PAGE_PRESENT | _PAGE_RW | _PAGE_ACCESSED |
> _PAGE_IOMAP);
> +
> +    while(nr_page) {
> +        batch = min(REMAP_BATCH_SIZE, nr);
> +        range = (unsigned long)batch << PAGE_SHIFT;
> +
> +        rmd.mmu_update = mmu_update;
> +
> +        for(i=0; i < batch; i++){
> +            pte = pte_mkspecial(pfn_pte(rmd.mfn++, rmd.prot));
> +            vaddr = base_addr + i*PAGE_SIZE;
> +            ptep = lookup_address(vaddr, &level);

you need to check if ptep is valid here and the level is PG_LEVEL_4K

> +            rmd.mmu_update->ptr = arbitrary_virt_to_machine(ptep).maddr |
> +                                        MMU_NORMAL_PT_UPDATE;

you can use pte_mfn(*ptep) instead of arbitrary_virt_to_machine


> +            rmd.mmu_update->val = pte_val_ma(pte);
> +            rmd.mmu_update++;
> +        }
> +
> +        err = -EFAULT;
> +        if(HYPERVISOR_mmu_update(mmu_update, batch, NULL, domid) < 0)
> +            goto out;
> +
> +        nr_page -= batch;
> +        base_addr += range;
> +    }
> +
> +    err = 0;
> +
> +    base_addr = addr;
> +    for(i=0; i < nr; i++){
> +        vaddr = base_addr + i*PAGE_SIZE;
> +        set_phys_to_machine(vmalloc_to_pfn(vaddr),
> +                arbitrary_virt_to_machine(vaddr).maddr >> PAGE_SHIFT);
> +    }

The second argument (mfn) to set_phys_to_machine is wrong:
arbitrary_virt_to_machine ends up calling virt_to_machine if
virt_addr_valid. You need to manually call pte_mfn:

/* the ptep content has been updated by Xen so we can lookup the foreign
 * mfn from the pte now */
pte = lookup_address(vaddr, &level);
BUG_ON(pte == NULL);
offset = vaddr & ~PAGE_MASK;
mfn = XMADDR(((phys_addr_t)pte_mfn(*pte) << PAGE_SHIFT) + offset);


> +
> +out:
> +     flush_tlb_all();
> +     return err;
> +}
> +EXPORT_SYMBOL_GPL(xen_remap_domain_mfn_range2);

the name should be changed to xen_remap_foreign_gpfn_range


>  #ifdef CONFIG_XEN_PVHVM
>  static void xen_hvm_exit_mmap(struct mm_struct *mm)
>  {
> diff --git a/drivers/video/xen-fbfront.c b/drivers/video/xen-fbfront.c
> index dc72563..82da2ee 100644
> --- a/drivers/video/xen-fbfront.c
> +++ b/drivers/video/xen-fbfront.c
> @@ -25,8 +25,12 @@
>  #include <linux/module.h>
>  #include <linux/vmalloc.h>
>  #include <linux/mm.h>
> +#include <linux/sched.h>
> +#include <asm/pgtable.h>
> +#include <asm/page.h>
> 
>  #include <asm/xen/hypervisor.h>
> +#include <asm/xen/page.h>
> 
>  #include <xen/xen.h>
>  #include <xen/events.h>
> @@ -34,6 +38,7 @@
>  #include <xen/interface/io/fbif.h>
>  #include <xen/interface/io/protocols.h>
>  #include <xen/xenbus.h>
> +#include <xen/xen-ops.h>
> 
>  struct xenfb_info {
>       unsigned char           *fb;
> @@ -62,6 +67,12 @@ module_param_array(video, int, NULL, 0);
>  MODULE_PARM_DESC(video,
>       "Video memory size in MB, width, height in pixels (default 2,800,600)");
> 
> +static unsigned long foreign_vaddr = 0;
> +module_param(foreign_vaddr, ulong, S_IRUGO);
> +
> +static unsigned long foreign_domid = 0;
> +module_param(foreign_domid, ulong, S_IRUGO);
> +
>  static void xenfb_make_preferred_console(void);
>  static int xenfb_remove(struct xenbus_device *);
>  static void xenfb_init_shared_page(struct xenfb_info *, struct fb_info *);
> @@ -398,7 +408,17 @@ static int __devinit xenfb_probe(struct xenbus_device 
> *dev,
>       if (info->fb == NULL)
>               goto error_nomem;
>       memset(info->fb, 0, fb_size);
> -
> +    if((foreign_vaddr != 0) && (foreign_domid != 0)){
> +        ret = xen_remap_domain_mfn_range2((unsigned long)(info->fb),
> +                                    foreign_vaddr >> PAGE_SHIFT,
> +                                    fb_size >> PAGE_SHIFT, foreign_domid);

you should rename foreign_vaddr to foreign_gpfn and pass the gpfn value
that is the ram_addr (page shifted) passed to xen_ram_alloc in qemu.

> +        if(ret < 0){
> +            printk("Can not remap vram of hvm guest.\n");
> +            goto error;
> +        }
> +    }
>       info->nr_pages = (fb_size + PAGE_SIZE - 1) >> PAGE_SHIFT;
> 
>       info->mfns = vmalloc(sizeof(unsigned long) * info->nr_pages);
> diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
> index 4349e89..1554531 100644
> --- a/include/xen/xen-ops.h
> +++ b/include/xen/xen-ops.h
> @@ -20,6 +20,10 @@ int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
>                              unsigned long mfn, int nr,
>                              pgprot_t prot, unsigned domid);
> 
> +int xen_remap_domain_mfn_range2(unsigned long addr,unsigned long mfn,
> +                int nr, unsigned domid);
>  extern unsigned long *xen_contiguous_bitmap;
>  int xen_create_contiguous_region(unsigned long vstart, unsigned int order,
>                               unsigned int address_bits);
> 

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