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Re: [Xen-devel] [PATCH v2 01/25] arm/altp2m: Add first altp2m HVMOP stubs.





On 04/08/16 17:01, Sergej Proskurin wrote:
Hi Julien,


On 08/03/2016 06:54 PM, Julien Grall wrote:
Hello Sergej,

On 01/08/16 18:10, Sergej Proskurin wrote:
This commit moves the altp2m-related code from x86 to ARM. Functions
that are no yet supported notify the caller or print a BUG message
stating their absence.

Also, the struct arch_domain is extended with the altp2m_active
attribute, representing the current altp2m activity configuration of the
domain.

Signed-off-by: Sergej Proskurin <proskurin@xxxxxxxxxxxxx>
---
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
---
v2: Removed altp2m command-line option: Guard through HVM_PARAM_ALTP2M.
    Removed not used altp2m helper stubs in altp2m.h.
---
 xen/arch/arm/hvm.c           | 79
++++++++++++++++++++++++++++++++++++++++++++
 xen/include/asm-arm/altp2m.h |  4 +--
 xen/include/asm-arm/domain.h |  3 ++
 3 files changed, 84 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/hvm.c b/xen/arch/arm/hvm.c
index d999bde..eb524ae 100644
--- a/xen/arch/arm/hvm.c
+++ b/xen/arch/arm/hvm.c
@@ -32,6 +32,81 @@

 #include <asm/hypercall.h>

+#include <asm/altp2m.h>
+
+static int do_altp2m_op(XEN_GUEST_HANDLE_PARAM(void) arg)
+{
+    struct xen_hvm_altp2m_op a;
+    struct domain *d = NULL;
+    int rc = 0;
+
+    if ( copy_from_guest(&a, arg, 1) )
+        return -EFAULT;
+
+    if ( a.pad1 || a.pad2 ||
+         (a.version != HVMOP_ALTP2M_INTERFACE_VERSION) ||
+         (a.cmd < HVMOP_altp2m_get_domain_state) ||
+         (a.cmd > HVMOP_altp2m_change_gfn) )
+        return -EINVAL;
+
+    d = (a.cmd != HVMOP_altp2m_vcpu_enable_notify) ?
+        rcu_lock_domain_by_any_id(a.domain) :
rcu_lock_current_domain();
+
+    if ( d == NULL )
+        return -ESRCH;
+
+    if ( (a.cmd != HVMOP_altp2m_get_domain_state) &&
+         (a.cmd != HVMOP_altp2m_set_domain_state) &&
+         !d->arch.altp2m_active )

Why not using altp2m_active(d) here?


I have already changed that within the next patch version. Thank you.

Also this check looks quite racy. What does prevent another CPU to
disable altp2m at the same time? How the code would behave?


Thank you. I will protect this part with the altp2m_lock.

I have noticed that you use the altp2m_lock (it is a spinlock) in multiple places. So you will serialize a lot of code. Is it fine for you?

Regards,

--
Julien Grall

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