Re: [Xen-devel] [PATCH v4 08/16] xen/mm: Drop the parameter mfn from populate_pt_range

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Mar 05, 2018 at 07:38:36AM -0700, Jan Beulich wrote:
> >>> On 05.03.18 at 15:11, <julien.grall@xxxxxxx> wrote:
> > On 05/03/18 14:00, Jan Beulich wrote:
> >>>>> On 05.03.18 at 14:43, <julien.grall@xxxxxxx> wrote:
> >>> Anyway, I don't have much knowledge on the x86 to make the modification
> >>> that you suggested. So I am going to revert to _mfn(0) for x86.
> >> 
> >> I'd prefer if you didn't, but well, it'll be one of us to clean it up
> >> then.
> > I can keep as INVALID_MFN. But then either you or Andrew (or anyone x86 
> > folks) would have to provide the patch to skip incrementing invalid MFN 
> > (if I understood correctly your request).
> 
> Sigh - this should go together imo. While wrongly incrementing from
> zero was bad, wrongly wrapping from INVALID_MFN makes things
> worse.
> 

Try this patch?

---8<---
From 8f0024c690c736d17adde0fa765cbbf6fa2846dc Mon Sep 17 00:00:00 2001
From: Wei Liu <wei.liu2@xxxxxxxxxx>
Date: Fri, 9 Mar 2018 17:20:14 +0000
Subject: [PATCH] x86/mm: skip incrementing mfn if it is not a valid mfn

The function is called to fill in page table entries in
populate_pt_range. Skip incrementing mfn if it is invalid.

Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 xen/arch/x86/mm.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 9b559448a7..5f5577c7c2 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -4731,7 +4731,8 @@ int map_pages_to_xen(
             }
 
             virt    += 1UL << L3_PAGETABLE_SHIFT;
-            mfn     += 1UL << (L3_PAGETABLE_SHIFT - PAGE_SHIFT);
+            if ( !mfn_eq(_mfn(mfn), INVALID_MFN) )
+                mfn += 1UL << (L3_PAGETABLE_SHIFT - PAGE_SHIFT);
             nr_mfns -= 1UL << (L3_PAGETABLE_SHIFT - PAGE_SHIFT);
             continue;
         }
@@ -4756,7 +4757,8 @@ int map_pages_to_xen(
                 if ( i > nr_mfns )
                     i = nr_mfns;
                 virt    += i << PAGE_SHIFT;
-                mfn     += i;
+                if ( !mfn_eq(_mfn(mfn), INVALID_MFN) )
+                    mfn += i;
                 nr_mfns -= i;
                 continue;
             }
@@ -4824,7 +4826,8 @@ int map_pages_to_xen(
             }
 
             virt    += 1UL << L2_PAGETABLE_SHIFT;
-            mfn     += 1UL << PAGETABLE_ORDER;
+            if ( !mfn_eq(_mfn(mfn), INVALID_MFN) )
+                mfn += 1UL << PAGETABLE_ORDER;
             nr_mfns -= 1UL << PAGETABLE_ORDER;
         }
         else
@@ -4853,7 +4856,8 @@ int map_pages_to_xen(
                     if ( i > nr_mfns )
                         i = nr_mfns;
                     virt    += i << L1_PAGETABLE_SHIFT;
-                    mfn     += i;
+                    if ( !mfn_eq(_mfn(mfn), INVALID_MFN) )
+                        mfn += i;
                     nr_mfns -= i;
                     goto check_l3;
                 }
@@ -4898,7 +4902,8 @@ int map_pages_to_xen(
             }
 
             virt    += 1UL << L1_PAGETABLE_SHIFT;
-            mfn     += 1UL;
+            if ( !mfn_eq(_mfn(mfn), INVALID_MFN) )
+                mfn += 1UL;
             nr_mfns -= 1UL;
 
             if ( (flags == PAGE_HYPERVISOR) &&
-- 
2.11.0


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