Re: [Xen-devel] [PATCH v4] xen/grant-table: Avoid m2p_override duringmapping

From: Zoltan Kiss
Date: Thu Jan 23 2014 - 10:12:18 EST

On 23/01/14 13:59, Stefano Stabellini wrote:
On Wed, 22 Jan 2014, Zoltan Kiss wrote:
diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 2ae8699..0060178 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -872,15 +872,13 @@ static unsigned long mfn_hash(unsigned long mfn)

/* Add an MFN override for a particular page */
int m2p_add_override(unsigned long mfn, struct page *page,
- struct gnttab_map_grant_ref *kmap_op)
+ struct gnttab_map_grant_ref *kmap_op, unsigned long

Do we really need to add another additional parameter to
I would just let m2p_add_override and m2p_remove_override call
page_to_pfn again. It is not that expensive.
Yes, because that page_to_pfn can return something different. That's why
v2 patches failed.

I am really curious: how can page_to_pfn return something different?
I don't think is supposed to happen.
You call set_phys_to_machine before calling m2p* functions.

set_phys_to_machine changes the physical to machine mapping, that would
be the mfn corresponding to a given pfn. It shouldn't affect the output
of page_to_pfn that returns the pfn corresponding to a given struct
page. The calculation of which is based on address offsets and should be
static and unaffected by things like set_phys_to_machine.

Indeed, my mistake. The mfn is the only thing which changes, it still has to be passed to m2p_remove_override. I'll send in a next version


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