Re: [PATCH 4/6] xen-gntdev: Support mapping in HVM domains

[Daniel De Graaf <dgdegra@tycho.nsa.gov>]

On 01/27/2011 01:52 PM, Konrad Rzeszutek Wilk wrote:
> On Fri, Jan 21, 2011 at 10:59:06AM -0500, Daniel De Graaf wrote:
>> HVM does not allow direct PTE modification, so instead we request
>> that Xen change its internal p2m mappings on the allocated pages and
>> map the memory into userspace normally.
>>
>> Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
>> ---
>>  drivers/xen/gntdev.c      |  115 +++++++++++++++++++++++++++++++-------------
>>  drivers/xen/grant-table.c |    6 ++
>>  2 files changed, 87 insertions(+), 34 deletions(-)
>>
>> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
>> index 256162b..a5710e8 100644
>> --- a/drivers/xen/gntdev.c
>> +++ b/drivers/xen/gntdev.c
>> @@ -32,6 +32,7 @@
>>  #include <linux/sched.h>
>>  #include <linux/spinlock.h>
>>  #include <linux/slab.h>
>> +#include <linux/highmem.h>
>>  
>>  #include <xen/xen.h>
>>  #include <xen/grant_table.h>
>> @@ -52,6 +53,8 @@ MODULE_PARM_DESC(limit, "Maximum number of grants that may be mapped by "
>>  
>>  static atomic_t pages_mapped = ATOMIC_INIT(0);
>>  
>> +static int use_ptemod;
>> +
>>  struct gntdev_priv {
>>  	struct list_head maps;
>>  	/* lock protects maps from concurrent changes */
>> @@ -74,6 +77,8 @@ struct grant_map {
>>  	struct page **pages;
>>  };
>>  
>> +static int unmap_grant_pages(struct grant_map *map, int offset, int pages);
>> +
>>  /* ------------------------------------------------------------------ */
>>  
>>  static void gntdev_print_maps(struct gntdev_priv *priv,
>> @@ -179,11 +184,32 @@ static void gntdev_put_map(struct grant_map *map)
>>  
>>  	atomic_sub(map->count, &pages_mapped);
>>  
>> -	if (map->pages)
>> +	if (map->pages) {
>> +		if (!use_ptemod)
>> +			unmap_grant_pages(map, 0, map->count);
>> +
>>  		for (i = 0; i < map->count; i++) {
>> -			if (map->pages[i])
>> +			uint32_t check, *tmp;
>> +			if (!map->pages[i])
>> +				continue;
>> +			/* XXX When unmapping in an HVM domain, Xen will
>> +			 * sometimes end up mapping the GFN to an invalid MFN.
>> +			 * In this case, writes will be discarded and reads will
>> +			 * return all 0xFF bytes.  Leak these unusable GFNs
> 
> I forgot to ask, under what version of Xen did you run this? I want to add
> that to the comment so when it gets fixed we know what the failing version is.

4.1-unstable. In particular, 22641:4e108cf56d07 exhibits the bug, and I have not
found a version of 4.1 that doesn't (although I haven't searched for that in
particular). I could try to find other versions also exhibit this behavior, if
it would be useful to have a list.

Note for reproducing: at r22641, you need to revert 22402:7d2fdc083c9c or the
grant table of the HVM guest will not be readable by Xen. My test that exercises
the bug is an HVM-to-HVM grant.

>> +			 * until Xen supports fixing their p2m mapping.
>> +			 */
>> +			tmp = kmap(map->pages[i]);
>> +			*tmp = 0xdeaddead;
>> +			mb();
>> +			check = *tmp;
>> +			kunmap(map->pages[i]);
>> +			if (check == 0xdeaddead)
>>  				__free_page(map->pages[i]);
>> +			else
>> +				pr_debug("Discard page %d=%ld\n", i,
>> +					page_to_pfn(map->pages[i]));
>>  		}
>> +	}
>>  	kfree(map->pages);
>>  	kfree(map->grants);
>>  	kfree(map->map_ops);
>> @@ -198,17 +224,16 @@ static int find_grant_ptes(pte_t *pte, pgtable_t token,
>>  {
>>  	struct grant_map *map = data;
>>  	unsigned int pgnr = (addr - map->vma->vm_start) >> PAGE_SHIFT;
>> +	int flags = map->flags | GNTMAP_application_map | GNTMAP_contains_pte;
>>  	u64 pte_maddr;
>>  
>>  	BUG_ON(pgnr >= map->count);
>>  	pte_maddr = arbitrary_virt_to_machine(pte).maddr;
>>  
>> -	gnttab_set_map_op(&map->map_ops[pgnr], pte_maddr,
>> -			  GNTMAP_contains_pte | map->flags,
>> +	gnttab_set_map_op(&map->map_ops[pgnr], pte_maddr, flags,
>>  			  map->grants[pgnr].ref,
>>  			  map->grants[pgnr].domid);
>> -	gnttab_set_unmap_op(&map->unmap_ops[pgnr], pte_maddr,
>> -			    GNTMAP_contains_pte | map->flags,
>> +	gnttab_set_unmap_op(&map->unmap_ops[pgnr], pte_maddr, flags,
>>  			    0 /* handle */);
>>  	return 0;
>>  }
>> @@ -216,6 +241,19 @@ static int find_grant_ptes(pte_t *pte, pgtable_t token,
>>  static int map_grant_pages(struct grant_map *map)
>>  {
>>  	int i, err = 0;
>> +	phys_addr_t addr;
>> +
>> +	if (!use_ptemod) {
>> +		for (i = 0; i < map->count; i++) {
>> +			addr = (phys_addr_t)
>> +				pfn_to_kaddr(page_to_pfn(map->pages[i]));
>> +			gnttab_set_map_op(&map->map_ops[i], addr, map->flags,
>> +				map->grants[i].ref,
>> +				map->grants[i].domid);
>> +			gnttab_set_unmap_op(&map->unmap_ops[i], addr,
>> +				map->flags, 0 /* handle */);
>> +		}
>> +	}
>>  
>>  	pr_debug("map %d+%d\n", map->index, map->count);
>>  	err = gnttab_map_refs(map->map_ops, map->pages, map->count);
>> @@ -260,17 +298,8 @@ static void gntdev_vma_close(struct vm_area_struct *vma)
>>  	gntdev_put_map(map);
>>  }
>>  
>> -static int gntdev_vma_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
>> -{
>> -	pr_debug("vaddr %p, pgoff %ld (shouldn't happen)\n",
>> -			vmf->virtual_address, vmf->pgoff);
>> -	vmf->flags = VM_FAULT_ERROR;
>> -	return 0;
>> -}
>> -
>>  static struct vm_operations_struct gntdev_vmops = {
>>  	.close = gntdev_vma_close,
>> -	.fault = gntdev_vma_fault,
>>  };
>>  
>>  /* ------------------------------------------------------------------ */
>> @@ -355,14 +384,16 @@ static int gntdev_open(struct inode *inode, struct file *flip)
>>  	INIT_LIST_HEAD(&priv->maps);
>>  	spin_lock_init(&priv->lock);
>>  
>> -	priv->mm = get_task_mm(current);
>> -	if (!priv->mm) {
>> -		kfree(priv);
>> -		return -ENOMEM;
>> +	if (use_ptemod) {
>> +		priv->mm = get_task_mm(current);
>> +		if (!priv->mm) {
>> +			kfree(priv);
>> +			return -ENOMEM;
>> +		}
>> +		priv->mn.ops = &gntdev_mmu_ops;
>> +		ret = mmu_notifier_register(&priv->mn, priv->mm);
>> +		mmput(priv->mm);
>>  	}
>> -	priv->mn.ops = &gntdev_mmu_ops;
>> -	ret = mmu_notifier_register(&priv->mn, priv->mm);
>> -	mmput(priv->mm);
>>  
>>  	if (ret) {
>>  		kfree(priv);
>> @@ -390,7 +421,8 @@ static int gntdev_release(struct inode *inode, struct file *flip)
>>  	}
>>  	spin_unlock(&priv->lock);
>>  
>> -	mmu_notifier_unregister(&priv->mn, priv->mm);
>> +	if (use_ptemod)
>> +		mmu_notifier_unregister(&priv->mn, priv->mm);
>>  	kfree(priv);
>>  	return 0;
>>  }
>> @@ -515,7 +547,7 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>>  	int index = vma->vm_pgoff;
>>  	int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
>>  	struct grant_map *map;
>> -	int err = -EINVAL;
>> +	int i, err = -EINVAL;
>>  
>>  	if ((vma->vm_flags & VM_WRITE) && !(vma->vm_flags & VM_SHARED))
>>  		return -EINVAL;
>> @@ -527,9 +559,9 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>>  	map = gntdev_find_map_index(priv, index, count);
>>  	if (!map)
>>  		goto unlock_out;
>> -	if (map->vma)
>> +	if (use_ptemod && map->vma)
>>  		goto unlock_out;
>> -	if (priv->mm != vma->vm_mm) {
>> +	if (use_ptemod && priv->mm != vma->vm_mm) {
>>  		printk(KERN_WARNING "Huh? Other mm?\n");
>>  		goto unlock_out;
>>  	}
>> @@ -541,20 +573,24 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>>  	vma->vm_flags |= VM_RESERVED|VM_DONTCOPY|VM_DONTEXPAND|VM_PFNMAP;
>>  
>>  	vma->vm_private_data = map;
>> -	map->vma = vma;
>>  
>> -	map->flags = GNTMAP_host_map | GNTMAP_application_map;
>> +	if (use_ptemod)
>> +		map->vma = vma;
>> +
>> +	map->flags = GNTMAP_host_map;
>>  	if (!(vma->vm_flags & VM_WRITE))
>>  		map->flags |= GNTMAP_readonly;
>>  
>>  	spin_unlock(&priv->lock);
>>  
>> -	err = apply_to_page_range(vma->vm_mm, vma->vm_start,
>> -				  vma->vm_end - vma->vm_start,
>> -				  find_grant_ptes, map);
>> -	if (err) {
>> -		printk(KERN_WARNING "find_grant_ptes() failure.\n");
>> -		return err;
>> +	if (use_ptemod) {
>> +		err = apply_to_page_range(vma->vm_mm, vma->vm_start,
>> +					  vma->vm_end - vma->vm_start,
>> +					  find_grant_ptes, map);
>> +		if (err) {
>> +			printk(KERN_WARNING "find_grant_ptes() failure.\n");
>> +			return err;
>> +		}
>>  	}
>>  
>>  	err = map_grant_pages(map);
>> @@ -565,6 +601,15 @@ static int gntdev_mmap(struct file *flip, struct vm_area_struct *vma)
>>  
>>  	map->is_mapped = 1;
>>  
>> +	if (!use_ptemod) {
>> +		for (i = 0; i < count; i++) {
>> +			err = vm_insert_page(vma, vma->vm_start + i*PAGE_SIZE,
>> +				map->pages[i]);
>> +			if (err)
>> +				return err;
>> +		}
>> +	}
>> +
>>  	return 0;
>>  
>>  unlock_out:
>> @@ -595,6 +640,8 @@ static int __init gntdev_init(void)
>>  	if (!xen_domain())
>>  		return -ENODEV;
>>  
>> +	use_ptemod = xen_pv_domain();
>> +
>>  	err = misc_register(&gntdev_miscdev);
>>  	if (err != 0) {
>>  		printk(KERN_ERR "Could not register gntdev device\n");
>> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
>> index 9ef54eb..9428ced 100644
>> --- a/drivers/xen/grant-table.c
>> +++ b/drivers/xen/grant-table.c
>> @@ -458,6 +458,9 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
>>  	if (ret)
>>  		return ret;
>>  
>> +	if (xen_feature(XENFEAT_auto_translated_physmap))
>> +		return ret;
>> +
>>  	for (i = 0; i < count; i++) {
>>  		/* m2p override only supported for GNTMAP_contains_pte mappings */
>>  		if (!(map_ops[i].flags & GNTMAP_contains_pte))
>> @@ -483,6 +486,9 @@ int gnttab_unmap_refs(struct gnttab_unmap_grant_ref *unmap_ops,
>>  	if (ret)
>>  		return ret;
>>  
>> +	if (xen_feature(XENFEAT_auto_translated_physmap))
>> +		return ret;
>> +
>>  	for (i = 0; i < count; i++) {
>>  		ret = m2p_remove_override(pages[i]);
>>  		if (ret)
>> -- 
>> 1.7.3.4