[PATCH for-4.10 0/2] xen/arm: Add more debug in get_page_from_gva

[PATCH for-4.10 0/2] xen/arm: Add more debug in get_page_from_gva

[Julien Grall]

Hi all,

It looks like get_page_from_gva intermittenly fails on the Arndale (see [1])
leading to Dom0 crashing.

At the moment it is a bit hard to know why given the hypervisor does not
provide much information.

This series add more debug in get_page_from_gva to hopefully narrow down
the issue.

I think the 2 patches are good candidate for Xen 4.10 as this may help fixing
a dom0 crash on the Arndale.

Cheers,

[1] https://lists.xen.org/archives/html/xen-devel/2017-11/msg00942.html

Julien Grall (2):
  xen/arm: mm: Change the return value of gvirt_to_maddr
  xen/arm: p2m: Add more debug in get_page_from_gva

 xen/arch/arm/domain_build.c |  8 ++++----
 xen/arch/arm/kernel.c       |  8 ++++----
 xen/arch/arm/p2m.c          | 19 ++++++++++++++++---
 xen/include/asm-arm/mm.h    |  9 +++++++--
 4 files changed, 31 insertions(+), 13 deletions(-)

-- 
2.11.0


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[PATCH for-4.10 1/2] xen/arm: mm: Change the return value of gvirt_to_maddr

[Julien Grall]

Currently, gvirt_to_maddr return -EFAULT when the translation failed.
It might be useful to return the PAR_EL1 (Physical Address Register)
in such a case to get a better idea of the reason.

So modify the return value to use 0 on sucess or return the PAR on
failure.

The callers are modified to reflect the change of the return value.

Note that with the change in gvirt_to_maddr, ma needs to be initialized
to avoid GCC been confused (i.e value may be unitialized) with the new
construction.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
---
 xen/arch/arm/domain_build.c | 8 ++++----
 xen/arch/arm/kernel.c       | 8 ++++----
 xen/arch/arm/p2m.c          | 6 +++---
 xen/include/asm-arm/mm.h    | 9 +++++++--
 4 files changed, 18 insertions(+), 13 deletions(-)

diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
index bf29299707..c74f4dd69d 100644
--- a/xen/arch/arm/domain_build.c
+++ b/xen/arch/arm/domain_build.c
@@ -2002,15 +2002,15 @@ static void initrd_load(struct kernel_info *kinfo)
 
     for ( offs = 0; offs < len; )
     {
-        int rc;
-        paddr_t s, l, ma;
+        uint64_t par;
+        paddr_t s, l, ma = 0;
         void *dst;
 
         s = offs & ~PAGE_MASK;
         l = min(PAGE_SIZE - s, len);
 
-        rc = gvirt_to_maddr(load_addr + offs, &ma, GV2M_WRITE);
-        if ( rc )
+        par = gvirt_to_maddr(load_addr + offs, &ma, GV2M_WRITE);
+        if ( par )
         {
             panic("Unable to translate guest address");
             return;
diff --git a/xen/arch/arm/kernel.c b/xen/arch/arm/kernel.c
index c2755a9ab9..a6c6413712 100644
--- a/xen/arch/arm/kernel.c
+++ b/xen/arch/arm/kernel.c
@@ -167,15 +167,15 @@ static void kernel_zimage_load(struct kernel_info *info)
            paddr, load_addr, load_addr + len);
     for ( offs = 0; offs < len; )
     {
-        int rc;
-        paddr_t s, l, ma;
+        uint64_t par;
+        paddr_t s, l, ma = 0;
         void *dst;
 
         s = offs & ~PAGE_MASK;
         l = min(PAGE_SIZE - s, len);
 
-        rc = gvirt_to_maddr(load_addr + offs, &ma, GV2M_WRITE);
-        if ( rc )
+        par = gvirt_to_maddr(load_addr + offs, &ma, GV2M_WRITE);
+        if ( par )
         {
             panic("Unable to map translate guest address");
             return;
diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 68b488997d..f6b3d8e421 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -1414,7 +1414,7 @@ struct page_info *get_page_from_gva(struct vcpu *v, vaddr_t va,
     struct p2m_domain *p2m = p2m_get_hostp2m(d);
     struct page_info *page = NULL;
     paddr_t maddr = 0;
-    int rc;
+    uint64_t par;
 
     /*
      * XXX: To support a different vCPU, we would need to load the
@@ -1425,9 +1425,9 @@ struct page_info *get_page_from_gva(struct vcpu *v, vaddr_t va,
 
     p2m_read_lock(p2m);
 
-    rc = gvirt_to_maddr(va, &maddr, flags);
+    par = gvirt_to_maddr(va, &maddr, flags);
 
-    if ( rc )
+    if ( par )
         goto err;
 
     if ( !mfn_valid(maddr_to_mfn(maddr)) )
diff --git a/xen/include/asm-arm/mm.h b/xen/include/asm-arm/mm.h
index cd6dfb54b9..ad2f2a43dc 100644
--- a/xen/include/asm-arm/mm.h
+++ b/xen/include/asm-arm/mm.h
@@ -266,11 +266,16 @@ static inline void *maddr_to_virt(paddr_t ma)
 }
 #endif
 
-static inline int gvirt_to_maddr(vaddr_t va, paddr_t *pa, unsigned int flags)
+/*
+ * Translate a guest virtual address to a machine address.
+ * Return the fault information if the translation has failed else 0.
+ */
+static inline uint64_t gvirt_to_maddr(vaddr_t va, paddr_t *pa,
+                                      unsigned int flags)
 {
     uint64_t par = gva_to_ma_par(va, flags);
     if ( par & PAR_F )
-        return -EFAULT;
+        return par;
     *pa = (par & PADDR_MASK & PAGE_MASK) | ((unsigned long) va & ~PAGE_MASK);
     return 0;
 }
-- 
2.11.0


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[PATCH for-4.10 2/2] xen/arm: p2m: Add more debug in get_page_from_gva

[Julien Grall]

The function get_page_from_gva is used by copy_*_guest helpers to
translate a guest virtual address to a machine physical address and take
reference on the page.

There are a couple of errors path that will return the same value making
difficult to know the exact error. Add more debug in each error patch
only for debug-build.

This should help narrowing down the intermittent failure with the
hypercall GNTTABOP_copy (see [1]).

[1] https://lists.xen.org/archives/html/xen-devel/2017-11/msg00942.html

Signed-off-by: Julien Grall <julien.grall@linaro.org>
---
 xen/arch/arm/p2m.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index f6b3d8e421..417609ede2 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -1428,16 +1428,29 @@ struct page_info *get_page_from_gva(struct vcpu *v, vaddr_t va,
     par = gvirt_to_maddr(va, &maddr, flags);
 
     if ( par )
+    {
+        dprintk(XENLOG_G_DEBUG,
+                "%pv: gvirt_to_maddr failed va=%#"PRIvaddr" flags=0x%lx par=%#"PRIx64"\n",
+                v, va, flags, par);
         goto err;
+    }
 
     if ( !mfn_valid(maddr_to_mfn(maddr)) )
+    {
+        dprintk(XENLOG_G_DEBUG, "%pv: Invalid MFN %#"PRI_mfn"\n",
+                v, mfn_x(maddr_to_mfn(maddr)));
         goto err;
+    }
 
     page = mfn_to_page(maddr_to_mfn(maddr));
     ASSERT(page);
 
     if ( unlikely(!get_page(page, d)) )
+    {
+        dprintk(XENLOG_G_DEBUG, "%pv: Failing to acquire the MFN %#"PRI_mfn"\n",
+                v, mfn_x(maddr_to_mfn(maddr)));
         page = NULL;
+    }
 
 err:
     if ( !page && p2m->mem_access_enabled )
-- 
2.11.0


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Re: [PATCH for-4.10 2/2] xen/arm: p2m: Add more debug in get_page_from_gva

[Andrew Cooper]

On 15/11/17 19:34, Julien Grall wrote:
> The function get_page_from_gva is used by copy_*_guest helpers to
> translate a guest virtual address to a machine physical address and take
> reference on the page.
>
> There are a couple of errors path that will return the same value making
> difficult to know the exact error. Add more debug in each error patch
> only for debug-build.
>
> This should help narrowing down the intermittent failure with the
> hypercall GNTTABOP_copy (see [1]).
>
> [1] https://lists.xen.org/archives/html/xen-devel/2017-11/msg00942.html
>
> Signed-off-by: Julien Grall <julien.grall@linaro.org>
> ---
>  xen/arch/arm/p2m.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index f6b3d8e421..417609ede2 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -1428,16 +1428,29 @@ struct page_info *get_page_from_gva(struct vcpu *v, vaddr_t va,
>      par = gvirt_to_maddr(va, &maddr, flags);
>  
>      if ( par )
> +    {
> +        dprintk(XENLOG_G_DEBUG,
> +                "%pv: gvirt_to_maddr failed va=%#"PRIvaddr" flags=0x%lx par=%#"PRIx64"\n",
> +                v, va, flags, par);

Given the long round-trip time on debugging output, how about trying to
dump the guest and/or second stage table walk?

~Andrew

>          goto err;
> +    }
>  
>      if ( !mfn_valid(maddr_to_mfn(maddr)) )
> +    {
> +        dprintk(XENLOG_G_DEBUG, "%pv: Invalid MFN %#"PRI_mfn"\n",
> +                v, mfn_x(maddr_to_mfn(maddr)));
>          goto err;
> +    }
>  
>      page = mfn_to_page(maddr_to_mfn(maddr));
>      ASSERT(page);
>  
>      if ( unlikely(!get_page(page, d)) )
> +    {
> +        dprintk(XENLOG_G_DEBUG, "%pv: Failing to acquire the MFN %#"PRI_mfn"\n",
> +                v, mfn_x(maddr_to_mfn(maddr)));
>          page = NULL;
> +    }
>  
>  err:
>      if ( !page && p2m->mem_access_enabled )


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Re: [PATCH for-4.10 2/2] xen/arm: p2m: Add more debug in get_page_from_gva

[Julien Grall]

Hi Andrew,

On 11/15/2017 07:43 PM, Andrew Cooper wrote:
> On 15/11/17 19:34, Julien Grall wrote:
>> The function get_page_from_gva is used by copy_*_guest helpers to
>> translate a guest virtual address to a machine physical address and take
>> reference on the page.
>>
>> There are a couple of errors path that will return the same value making
>> difficult to know the exact error. Add more debug in each error patch
>> only for debug-build.
>>
>> This should help narrowing down the intermittent failure with the
>> hypercall GNTTABOP_copy (see [1]).
>>
>> [1] https://lists.xen.org/archives/html/xen-devel/2017-11/msg00942.html
>>
>> Signed-off-by: Julien Grall <julien.grall@linaro.org>
>> ---
>>   xen/arch/arm/p2m.c | 13 +++++++++++++
>>   1 file changed, 13 insertions(+)
>>
>> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
>> index f6b3d8e421..417609ede2 100644
>> --- a/xen/arch/arm/p2m.c
>> +++ b/xen/arch/arm/p2m.c
>> @@ -1428,16 +1428,29 @@ struct page_info *get_page_from_gva(struct vcpu *v, vaddr_t va,
>>       par = gvirt_to_maddr(va, &maddr, flags);
>>   
>>       if ( par )
>> +    {
>> +        dprintk(XENLOG_G_DEBUG,
>> +                "%pv: gvirt_to_maddr failed va=%#"PRIvaddr" flags=0x%lx par=%#"PRIx64"\n",
>> +                v, va, flags, par);
> 
> Given the long round-trip time on debugging output, how about trying to
> dump the guest and/or second stage table walk?

I thought about it, however at the moment dump_s1_guest_walk() is very 
minimal and would be add much value here. Thought, Now that we have code 
to do first-stage walk (see guest_walk_tables), we might be able to get 
a better dump here. Thought I am not sure it would be 4.10 material.

However, I think we could try to translate the guest VA to a guest PA 
using hardware instruction and then do the second-stage walk using 
dump_p2m_lookup.

Let me have a look.

Cheers,

-- 
Julien Grall

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Re: [PATCH for-4.10 1/2] xen/arm: mm: Change the return value of gvirt_to_maddr

[Stefano Stabellini]

On Wed, 15 Nov 2017, Julien Grall wrote:
> Currently, gvirt_to_maddr return -EFAULT when the translation failed.
> It might be useful to return the PAR_EL1 (Physical Address Register)
> in such a case to get a better idea of the reason.
> 
> So modify the return value to use 0 on sucess or return the PAR on
                                          ^ success


> failure.
> 
> The callers are modified to reflect the change of the return value.
> 
> Note that with the change in gvirt_to_maddr, ma needs to be initialized
> to avoid GCC been confused (i.e value may be unitialized) with the new
                                                 ^ uninitialized


> construction.
> 
> Signed-off-by: Julien Grall <julien.grall@linaro.org>

Acked-by: Stefano Stabellini <sstabellini@kernel.org>

I fixed on commit


> ---
>  xen/arch/arm/domain_build.c | 8 ++++----
>  xen/arch/arm/kernel.c       | 8 ++++----
>  xen/arch/arm/p2m.c          | 6 +++---
>  xen/include/asm-arm/mm.h    | 9 +++++++--
>  4 files changed, 18 insertions(+), 13 deletions(-)
> 
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index bf29299707..c74f4dd69d 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -2002,15 +2002,15 @@ static void initrd_load(struct kernel_info *kinfo)
>  
>      for ( offs = 0; offs < len; )
>      {
> -        int rc;
> -        paddr_t s, l, ma;
> +        uint64_t par;
> +        paddr_t s, l, ma = 0;
>          void *dst;
>  
>          s = offs & ~PAGE_MASK;
>          l = min(PAGE_SIZE - s, len);
>  
> -        rc = gvirt_to_maddr(load_addr + offs, &ma, GV2M_WRITE);
> -        if ( rc )
> +        par = gvirt_to_maddr(load_addr + offs, &ma, GV2M_WRITE);
> +        if ( par )
>          {
>              panic("Unable to translate guest address");
>              return;
> diff --git a/xen/arch/arm/kernel.c b/xen/arch/arm/kernel.c
> index c2755a9ab9..a6c6413712 100644
> --- a/xen/arch/arm/kernel.c
> +++ b/xen/arch/arm/kernel.c
> @@ -167,15 +167,15 @@ static void kernel_zimage_load(struct kernel_info *info)
>             paddr, load_addr, load_addr + len);
>      for ( offs = 0; offs < len; )
>      {
> -        int rc;
> -        paddr_t s, l, ma;
> +        uint64_t par;
> +        paddr_t s, l, ma = 0;
>          void *dst;
>  
>          s = offs & ~PAGE_MASK;
>          l = min(PAGE_SIZE - s, len);
>  
> -        rc = gvirt_to_maddr(load_addr + offs, &ma, GV2M_WRITE);
> -        if ( rc )
> +        par = gvirt_to_maddr(load_addr + offs, &ma, GV2M_WRITE);
> +        if ( par )
>          {
>              panic("Unable to map translate guest address");
>              return;
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index 68b488997d..f6b3d8e421 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -1414,7 +1414,7 @@ struct page_info *get_page_from_gva(struct vcpu *v, vaddr_t va,
>      struct p2m_domain *p2m = p2m_get_hostp2m(d);
>      struct page_info *page = NULL;
>      paddr_t maddr = 0;
> -    int rc;
> +    uint64_t par;
>  
>      /*
>       * XXX: To support a different vCPU, we would need to load the
> @@ -1425,9 +1425,9 @@ struct page_info *get_page_from_gva(struct vcpu *v, vaddr_t va,
>  
>      p2m_read_lock(p2m);
>  
> -    rc = gvirt_to_maddr(va, &maddr, flags);
> +    par = gvirt_to_maddr(va, &maddr, flags);
>  
> -    if ( rc )
> +    if ( par )
>          goto err;
>  
>      if ( !mfn_valid(maddr_to_mfn(maddr)) )
> diff --git a/xen/include/asm-arm/mm.h b/xen/include/asm-arm/mm.h
> index cd6dfb54b9..ad2f2a43dc 100644
> --- a/xen/include/asm-arm/mm.h
> +++ b/xen/include/asm-arm/mm.h
> @@ -266,11 +266,16 @@ static inline void *maddr_to_virt(paddr_t ma)
>  }
>  #endif
>  
> -static inline int gvirt_to_maddr(vaddr_t va, paddr_t *pa, unsigned int flags)
> +/*
> + * Translate a guest virtual address to a machine address.
> + * Return the fault information if the translation has failed else 0.
> + */
> +static inline uint64_t gvirt_to_maddr(vaddr_t va, paddr_t *pa,
> +                                      unsigned int flags)
>  {
>      uint64_t par = gva_to_ma_par(va, flags);
>      if ( par & PAR_F )
> -        return -EFAULT;
> +        return par;
>      *pa = (par & PADDR_MASK & PAGE_MASK) | ((unsigned long) va & ~PAGE_MASK);
>      return 0;
>  }
> -- 
> 2.11.0
> 

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Re: [PATCH for-4.10 2/2] xen/arm: p2m: Add more debug in get_page_from_gva

[Stefano Stabellini]

On Wed, 15 Nov 2017, Julien Grall wrote:
> The function get_page_from_gva is used by copy_*_guest helpers to
> translate a guest virtual address to a machine physical address and take
> reference on the page.
> 
> There are a couple of errors path that will return the same value making
                               ^ paths

> difficult to know the exact error. Add more debug in each error patch
^ it difficult


> only for debug-build.
> 
> This should help narrowing down the intermittent failure with the
> hypercall GNTTABOP_copy (see [1]).
> 
> [1] https://lists.xen.org/archives/html/xen-devel/2017-11/msg00942.html
> 
> Signed-off-by: Julien Grall <julien.grall@linaro.org>

Acked-by: Stefano Stabellini <sstabellini@kernel.org>

fixed on commit


> ---
>  xen/arch/arm/p2m.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> index f6b3d8e421..417609ede2 100644
> --- a/xen/arch/arm/p2m.c
> +++ b/xen/arch/arm/p2m.c
> @@ -1428,16 +1428,29 @@ struct page_info *get_page_from_gva(struct vcpu *v, vaddr_t va,
>      par = gvirt_to_maddr(va, &maddr, flags);
>  
>      if ( par )
> +    {
> +        dprintk(XENLOG_G_DEBUG,
> +                "%pv: gvirt_to_maddr failed va=%#"PRIvaddr" flags=0x%lx par=%#"PRIx64"\n",
> +                v, va, flags, par);
>          goto err;
> +    }
>  
>      if ( !mfn_valid(maddr_to_mfn(maddr)) )
> +    {
> +        dprintk(XENLOG_G_DEBUG, "%pv: Invalid MFN %#"PRI_mfn"\n",
> +                v, mfn_x(maddr_to_mfn(maddr)));
>          goto err;
> +    }
>  
>      page = mfn_to_page(maddr_to_mfn(maddr));
>      ASSERT(page);
>  
>      if ( unlikely(!get_page(page, d)) )
> +    {
> +        dprintk(XENLOG_G_DEBUG, "%pv: Failing to acquire the MFN %#"PRI_mfn"\n",
> +                v, mfn_x(maddr_to_mfn(maddr)));
>          page = NULL;
> +    }
>  
>  err:
>      if ( !page && p2m->mem_access_enabled )

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Re: [PATCH for-4.10 2/2] xen/arm: p2m: Add more debug in get_page_from_gva

[Julien Grall]

On 11/16/2017 01:36 AM, Stefano Stabellini wrote:
> On Wed, 15 Nov 2017, Julien Grall wrote:
>> The function get_page_from_gva is used by copy_*_guest helpers to
>> translate a guest virtual address to a machine physical address and take
>> reference on the page.
>>
>> There are a couple of errors path that will return the same value making
>                                 ^ paths
> 
>> difficult to know the exact error. Add more debug in each error patch
> ^ it difficult
> 
> 
>> only for debug-build.
>>
>> This should help narrowing down the intermittent failure with the
>> hypercall GNTTABOP_copy (see [1]).
>>
>> [1] https://lists.xen.org/archives/html/xen-devel/2017-11/msg00942.html
>>
>> Signed-off-by: Julien Grall <julien.grall@linaro.org>
> 
> Acked-by: Stefano Stabellini <sstabellini@kernel.org>
> 
> fixed on commit

I am not sure why this was merged given Andrew gave some comments...

> 
> 
>> ---
>>   xen/arch/arm/p2m.c | 13 +++++++++++++
>>   1 file changed, 13 insertions(+)
>>
>> diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
>> index f6b3d8e421..417609ede2 100644
>> --- a/xen/arch/arm/p2m.c
>> +++ b/xen/arch/arm/p2m.c
>> @@ -1428,16 +1428,29 @@ struct page_info *get_page_from_gva(struct vcpu *v, vaddr_t va,
>>       par = gvirt_to_maddr(va, &maddr, flags);
>>   
>>       if ( par )
>> +    {
>> +        dprintk(XENLOG_G_DEBUG,
>> +                "%pv: gvirt_to_maddr failed va=%#"PRIvaddr" flags=0x%lx par=%#"PRIx64"\n",
>> +                v, va, flags, par);
>>           goto err;
>> +    }
>>   
>>       if ( !mfn_valid(maddr_to_mfn(maddr)) )
>> +    {
>> +        dprintk(XENLOG_G_DEBUG, "%pv: Invalid MFN %#"PRI_mfn"\n",
>> +                v, mfn_x(maddr_to_mfn(maddr)));
>>           goto err;
>> +    }
>>   
>>       page = mfn_to_page(maddr_to_mfn(maddr));
>>       ASSERT(page);
>>   
>>       if ( unlikely(!get_page(page, d)) )
>> +    {
>> +        dprintk(XENLOG_G_DEBUG, "%pv: Failing to acquire the MFN %#"PRI_mfn"\n",
>> +                v, mfn_x(maddr_to_mfn(maddr)));
>>           page = NULL;
>> +    }
>>   
>>   err:
>>       if ( !page && p2m->mem_access_enabled )

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Re: [PATCH for-4.10 2/2] xen/arm: p2m: Add more debug in get_page_from_gva

[Stefano Stabellini]

On Thu, 16 Nov 2017, Julien Grall wrote:
> On 11/16/2017 01:36 AM, Stefano Stabellini wrote:
> > On Wed, 15 Nov 2017, Julien Grall wrote:
> > > The function get_page_from_gva is used by copy_*_guest helpers to
> > > translate a guest virtual address to a machine physical address and take
> > > reference on the page.
> > > 
> > > There are a couple of errors path that will return the same value making
> >                                 ^ paths
> > 
> > > difficult to know the exact error. Add more debug in each error patch
> > ^ it difficult
> > 
> > 
> > > only for debug-build.
> > > 
> > > This should help narrowing down the intermittent failure with the
> > > hypercall GNTTABOP_copy (see [1]).
> > > 
> > > [1] https://lists.xen.org/archives/html/xen-devel/2017-11/msg00942.html
> > > 
> > > Signed-off-by: Julien Grall <julien.grall@linaro.org>
> > 
> > Acked-by: Stefano Stabellini <sstabellini@kernel.org>
> > 
> > fixed on commit
> 
> I am not sure why this was merged given Andrew gave some comments...

Sorry Andrew! I missed your reply!

 
> > 
> > > ---
> > >   xen/arch/arm/p2m.c | 13 +++++++++++++
> > >   1 file changed, 13 insertions(+)
> > > 
> > > diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
> > > index f6b3d8e421..417609ede2 100644
> > > --- a/xen/arch/arm/p2m.c
> > > +++ b/xen/arch/arm/p2m.c
> > > @@ -1428,16 +1428,29 @@ struct page_info *get_page_from_gva(struct vcpu
> > > *v, vaddr_t va,
> > >       par = gvirt_to_maddr(va, &maddr, flags);
> > >         if ( par )
> > > +    {
> > > +        dprintk(XENLOG_G_DEBUG,
> > > +                "%pv: gvirt_to_maddr failed va=%#"PRIvaddr" flags=0x%lx
> > > par=%#"PRIx64"\n",
> > > +                v, va, flags, par);
> > >           goto err;
> > > +    }
> > >         if ( !mfn_valid(maddr_to_mfn(maddr)) )
> > > +    {
> > > +        dprintk(XENLOG_G_DEBUG, "%pv: Invalid MFN %#"PRI_mfn"\n",
> > > +                v, mfn_x(maddr_to_mfn(maddr)));
> > >           goto err;
> > > +    }
> > >         page = mfn_to_page(maddr_to_mfn(maddr));
> > >       ASSERT(page);
> > >         if ( unlikely(!get_page(page, d)) )
> > > +    {
> > > +        dprintk(XENLOG_G_DEBUG, "%pv: Failing to acquire the MFN
> > > %#"PRI_mfn"\n",
> > > +                v, mfn_x(maddr_to_mfn(maddr)));
> > >           page = NULL;
> > > +    }
> > >     err:
> > >       if ( !page && p2m->mem_access_enabled )
> 

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