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Re: [Xen-devel] [PATCH] xen/arm: dump guest stack even if not the current VCPU

Hi Frediano,

Thank you for the patch.

On 20/10/2014 16:39, Frediano Ziglio wrote:
From: Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>

If show_guest_stack was called from Xen context (for instance hitting
'0' key on Xen console) get_page_from_gva was not able to get the
page returning NULL.
Detecting different domain and changing VTTBR register make
get_page_from_gva works for different domains.

Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>
  xen/arch/arm/p2m.c   | 7 ++++++-
  xen/arch/arm/traps.c | 2 +-
  2 files changed, 7 insertions(+), 2 deletions(-)

Tested manually on a D01 board. I actually have only dom0 so EL1 is
already pointing to the right domain. I have some doubt about the
is_idle_domain test inside p2m_load_VTTBR.

I guess this patch could be consider as a bug fix for Xen 4.5. It makes dump stack working when the dump domain key is hit.

I used the "unlikely" to avoid decreasing performances on the normal
cases, I'm fine if you remove them.

I'm fine with keeping the unlikely.

diff --git a/xen/arch/arm/p2m.c b/xen/arch/arm/p2m.c
index 1585d35..cf872fc 100644
--- a/xen/arch/arm/p2m.c
+++ b/xen/arch/arm/p2m.c
@@ -1178,7 +1178,8 @@ struct page_info *get_page_from_gva(struct
domain *d, vaddr_t va,
      struct page_info *page = NULL;
      paddr_t maddr;

-    ASSERT(d == current->domain);
+    if ( unlikely(d != current->domain) )
+        p2m_load_VTTBR(d);

The code between the 2 p2m_load_VTTBR should not interrupted by an interrupt. I send a similar patch (https://patches.linaro.org/38895/) for flush_tlb_domain.


I think taking the lock for the whole function is a bit too much here.
IHMO, the lock is only necessary for gvirt_to_maddr.

But this is 4.6 material if the patch reaches 4.5.


Julien Grall

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