Hi all,
this patch fixes the dom0 kernel crash when creating a VM.
Now I am able to create VMs successfully on 2.6.37 rc1, even though
without disk or network access.
---
xen: set vma flag VM_PFNMAP in the privcmd mmap file_op
Set VM_PFNMAP in the privcmd mmap file_op, rather than later in
xen_remap_domain_mfn_range when it is too late because
vma_wants_writenotify has already been called and vm_page_prot has
already been modified.
Signed-off-by: Stefano Stabellini <[email protected]>
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index c237b81..2be1f36 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -2627,7 +2627,7 @@ int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
prot = __pgprot(pgprot_val(prot) | _PAGE_IOMAP);
- vma->vm_flags |= VM_IO | VM_RESERVED | VM_PFNMAP;
+ BUG_ON(!(vma->vm_flags & (VM_PFNMAP | VM_RESERVED | VM_IO)));
rmd.mfn = mfn;
rmd.prot = prot;
diff --git a/drivers/xen/xenfs/privcmd.c b/drivers/xen/xenfs/privcmd.c
index f80be7f..9aab216 100644
--- a/drivers/xen/xenfs/privcmd.c
+++ b/drivers/xen/xenfs/privcmd.c
@@ -385,7 +385,7 @@ static int privcmd_mmap(struct file *file, struct vm_area_struct *vma)
return -ENOSYS;
/* DONTCOPY is essential for Xen as copy_page_range is broken. */
- vma->vm_flags |= VM_RESERVED | VM_IO | VM_DONTCOPY;
+ vma->vm_flags |= VM_RESERVED | VM_IO | VM_DONTCOPY | VM_PFNMAP;
vma->vm_ops = &privcmd_vm_ops;
vma->vm_private_data = NULL;
On Thu, Nov 11, 2010 at 03:55:49PM +0000, Stefano Stabellini wrote:
> Hi all,
> this patch fixes the dom0 kernel crash when creating a VM.
> Now I am able to create VMs successfully on 2.6.37 rc1, even though
> without disk or network access.
>
> ---
>
> xen: set vma flag VM_PFNMAP in the privcmd mmap file_op
>
> Set VM_PFNMAP in the privcmd mmap file_op, rather than later in
> xen_remap_domain_mfn_range when it is too late because
> vma_wants_writenotify has already been called and vm_page_prot has
So vma_wants_writenotify sets the invalid flags on vma->vm_flags?
> already been modified.
By whom? vma_wants_writenotify looks to just return 0 or 1
Ah, depending on that return value it sets vma->vm_page_prot.
That looks odd, so if this:
1215 if (vma_wants_writenotify(vma))
1216 vma->vm_page_prot = vm_get_page_prot(vm_flags & ~VM_SHARED);
1217
does not set the vma->vm_page_prot we never set the vm_page_prot?
.. and it looks to not set that value earlier on either.
So VM_PFNMAP inhibits the mmap code from setting the vm_page_prot.
Is that what we want, not have vma->vm_page_prot set anything? Why?
>
> Signed-off-by: Stefano Stabellini <[email protected]>
>
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index c237b81..2be1f36 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -2627,7 +2627,7 @@ int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
>
> prot = __pgprot(pgprot_val(prot) | _PAGE_IOMAP);
>
> - vma->vm_flags |= VM_IO | VM_RESERVED | VM_PFNMAP;
> + BUG_ON(!(vma->vm_flags & (VM_PFNMAP | VM_RESERVED | VM_IO)));
>
> rmd.mfn = mfn;
> rmd.prot = prot;
> diff --git a/drivers/xen/xenfs/privcmd.c b/drivers/xen/xenfs/privcmd.c
> index f80be7f..9aab216 100644
> --- a/drivers/xen/xenfs/privcmd.c
> +++ b/drivers/xen/xenfs/privcmd.c
> @@ -385,7 +385,7 @@ static int privcmd_mmap(struct file *file, struct vm_area_struct *vma)
> return -ENOSYS;
>
> /* DONTCOPY is essential for Xen as copy_page_range is broken. */
> - vma->vm_flags |= VM_RESERVED | VM_IO | VM_DONTCOPY;
> + vma->vm_flags |= VM_RESERVED | VM_IO | VM_DONTCOPY | VM_PFNMAP;
> vma->vm_ops = &privcmd_vm_ops;
> vma->vm_private_data = NULL;
>
>
> _______________________________________________
> Xen-devel mailing list
> [email protected]
> http://lists.xensource.com/xen-devel
On 11/11/2010 08:40 AM, Konrad Rzeszutek Wilk wrote:
> On Thu, Nov 11, 2010 at 03:55:49PM +0000, Stefano Stabellini wrote:
>> Hi all,
>> this patch fixes the dom0 kernel crash when creating a VM.
>> Now I am able to create VMs successfully on 2.6.37 rc1, even though
>> without disk or network access.
>>
>> ---
>>
>> xen: set vma flag VM_PFNMAP in the privcmd mmap file_op
>>
>> Set VM_PFNMAP in the privcmd mmap file_op, rather than later in
>> xen_remap_domain_mfn_range when it is too late because
>> vma_wants_writenotify has already been called and vm_page_prot has
> So vma_wants_writenotify sets the invalid flags on vma->vm_flags?
>> already been modified.
> By whom? vma_wants_writenotify looks to just return 0 or 1
>
> Ah, depending on that return value it sets vma->vm_page_prot.
> That looks odd, so if this:
>
> 1215 if (vma_wants_writenotify(vma))
> 1216 vma->vm_page_prot = vm_get_page_prot(vm_flags & ~VM_SHARED);
> 1217
>
> does not set the vma->vm_page_prot we never set the vm_page_prot?
>
> .. and it looks to not set that value earlier on either.
>
> So VM_PFNMAP inhibits the mmap code from setting the vm_page_prot.
> Is that what we want, not have vma->vm_page_prot set anything? Why?
It is already set unconditionally earlier in mmap_region(). The
writenotify stuff will knobble the mapping to be RO so we can track the
first write with faults, but we don't want that in this case.
The VM_PFNMAP flag is generally correct anyway, since it means that the
mapping is of a random PFN which no corresponding struct page.
J
>> Signed-off-by: Stefano Stabellini <[email protected]>
>>
>> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
>> index c237b81..2be1f36 100644
>> --- a/arch/x86/xen/mmu.c
>> +++ b/arch/x86/xen/mmu.c
>> @@ -2627,7 +2627,7 @@ int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
>>
>> prot = __pgprot(pgprot_val(prot) | _PAGE_IOMAP);
>>
>> - vma->vm_flags |= VM_IO | VM_RESERVED | VM_PFNMAP;
>> + BUG_ON(!(vma->vm_flags & (VM_PFNMAP | VM_RESERVED | VM_IO)));
>>
>> rmd.mfn = mfn;
>> rmd.prot = prot;
>> diff --git a/drivers/xen/xenfs/privcmd.c b/drivers/xen/xenfs/privcmd.c
>> index f80be7f..9aab216 100644
>> --- a/drivers/xen/xenfs/privcmd.c
>> +++ b/drivers/xen/xenfs/privcmd.c
>> @@ -385,7 +385,7 @@ static int privcmd_mmap(struct file *file, struct vm_area_struct *vma)
>> return -ENOSYS;
>>
>> /* DONTCOPY is essential for Xen as copy_page_range is broken. */
>> - vma->vm_flags |= VM_RESERVED | VM_IO | VM_DONTCOPY;
>> + vma->vm_flags |= VM_RESERVED | VM_IO | VM_DONTCOPY | VM_PFNMAP;
>> vma->vm_ops = &privcmd_vm_ops;
>> vma->vm_private_data = NULL;
>>
>>
>> _______________________________________________
>> Xen-devel mailing list
>> [email protected]
>> http://lists.xensource.com/xen-devel
> _______________________________________________
> Xen-devel mailing list
> [email protected]
> http://lists.xensource.com/xen-devel
>
On Thu, 11 Nov 2010, Jeremy Fitzhardinge wrote:
> On 11/11/2010 08:40 AM, Konrad Rzeszutek Wilk wrote:
> > On Thu, Nov 11, 2010 at 03:55:49PM +0000, Stefano Stabellini wrote:
> >> Hi all,
> >> this patch fixes the dom0 kernel crash when creating a VM.
> >> Now I am able to create VMs successfully on 2.6.37 rc1, even though
> >> without disk or network access.
> >>
> >> ---
> >>
> >> xen: set vma flag VM_PFNMAP in the privcmd mmap file_op
> >>
> >> Set VM_PFNMAP in the privcmd mmap file_op, rather than later in
> >> xen_remap_domain_mfn_range when it is too late because
> >> vma_wants_writenotify has already been called and vm_page_prot has
> > So vma_wants_writenotify sets the invalid flags on vma->vm_flags?
> >> already been modified.
> > By whom? vma_wants_writenotify looks to just return 0 or 1
> >
> > Ah, depending on that return value it sets vma->vm_page_prot.
> > That looks odd, so if this:
> >
> > 1215 if (vma_wants_writenotify(vma))
> > 1216 vma->vm_page_prot = vm_get_page_prot(vm_flags & ~VM_SHARED);
> > 1217
> >
> > does not set the vma->vm_page_prot we never set the vm_page_prot?
> >
> > .. and it looks to not set that value earlier on either.
> >
> > So VM_PFNMAP inhibits the mmap code from setting the vm_page_prot.
> > Is that what we want, not have vma->vm_page_prot set anything? Why?
>
> It is already set unconditionally earlier in mmap_region(). The
> writenotify stuff will knobble the mapping to be RO so we can track the
> first write with faults, but we don't want that in this case.
>
exactly.
> The VM_PFNMAP flag is generally correct anyway, since it means that the
> mapping is of a random PFN which no corresponding struct page.
>
I think so too.
This is an update of the patch, with a more correct BUG_ON condition.
---
xen: set vma flag VM_PFNMAP in the privcmd mmap file_op
Set VM_PFNMAP in the privcmd mmap file_op, rather than later in
xen_remap_domain_mfn_range when it is too late because
vma_wants_writenotify has already been called and vm_page_prot has
already been modified.
Signed-off-by: Stefano Stabellini <[email protected]>
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index c237b81..f61b75d 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -2627,7 +2627,8 @@ int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
prot = __pgprot(pgprot_val(prot) | _PAGE_IOMAP);
- vma->vm_flags |= VM_IO | VM_RESERVED | VM_PFNMAP;
+ BUG_ON(!((vma->vm_flags & (VM_PFNMAP | VM_RESERVED | VM_IO)) ==
+ (VM_PFNMAP | VM_RESERVED | VM_IO)));
rmd.mfn = mfn;
rmd.prot = prot;
diff --git a/drivers/xen/xenfs/privcmd.c b/drivers/xen/xenfs/privcmd.c
index f80be7f..48f7b0f 100644
--- a/drivers/xen/xenfs/privcmd.c
+++ b/drivers/xen/xenfs/privcmd.c
@@ -384,8 +384,9 @@ static int privcmd_mmap(struct file *file, struct vm_area_struct *vma)
if (xen_feature(XENFEAT_auto_translated_physmap))
return -ENOSYS;
- /* DONTCOPY is essential for Xen as copy_page_range is broken. */
- vma->vm_flags |= VM_RESERVED | VM_IO | VM_DONTCOPY;
+ /* DONTCOPY is essential for Xen because copy_page_range doesn't know
+ * how to recreate these mappings */
+ vma->vm_flags |= VM_RESERVED | VM_IO | VM_DONTCOPY | VM_PFNMAP;
vma->vm_ops = &privcmd_vm_ops;
vma->vm_private_data = NULL;