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Re: [Xen-devel] [PATCH V5 08/10] xen: Call arch_domain_create() before evtchn_init()

Hi Chen,

On 30/05/2015 12:07, Chen Baozi wrote:
From: Chen Baozi <baozich@xxxxxxxxx>

evtchn_init() will call domain_max_vcpus() to allocate poll_mask, which
needs the max vCPU number returned by domain_max_vcpus(). On arm/arm64
platform, this number is determined by the vGIC the guest is going to
use, which won't be initialised until arch_domain_create() is finished.

Signed-off-by: Chen Baozi <baozich@xxxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
Cc: Tim Deegan <tim@xxxxxxx>
  xen/common/domain.c | 8 ++++----
  1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/xen/common/domain.c b/xen/common/domain.c
index 6803c4d..5b98f69 100644
--- a/xen/common/domain.c
+++ b/xen/common/domain.c
@@ -316,6 +316,10 @@ struct domain *domain_create(domid_t domid, unsigned int 
      if ( domcr_flags & DOMCRF_dummy )
          return d;

+    if ( (err = arch_domain_create(d, domcr_flags, config)) != 0 )
+        goto fail;
+    init_status |= INIT_arch;
      if ( !is_idle_domain(d) )
          if ( (err = xsm_domain_create(XSM_HOOK, d, ssidref)) != 0 )
@@ -354,10 +358,6 @@ struct domain *domain_create(domid_t domid, unsigned int 
              goto fail;

-    if ( (err = arch_domain_create(d, domcr_flags, config)) != 0 )
-        goto fail;
-    init_status |= INIT_arch;

NACK. Moving arch_domain_create means that we will allocate memory before checking the XSM policy. I don't think we want to execute an expensive function if the domain is not allowed to boot.

Furthermore, did you audit all the code to make sure that arch_domain_create (on both x86 and ARM) doesn't use the allocation done before (i.e evtch, grant table,...)?

Depending on this question, we may want to create a preinit domain creation with set the different value (such as the vGIC callback) without allocation memory.


Julien Grall

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