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[PATCH] xen/arm: add forward_smc command line option for debugging

It has become clear that an option to disable trapping SMC calls to Xen
is very useful for debugging user issues. Instead of having to provide a
patch to users every time, it would be great if we could just tell them
to add forward_smc=true to the Xen command line.

This option is obviously unsafe and unsecure and only meant for
debugging. Make clear in the description that if you pass
forward_smc=true then the system is not security supported.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>

diff --git a/docs/misc/xen-command-line.pandoc 
index 3ece83a427..0833fe80fc 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -2501,6 +2501,16 @@ vwfi to `native` reduces irq latency significantly. It 
can also lead to
 suboptimal scheduling decisions, but only when the system is
 oversubscribed (i.e., in total there are more vCPUs than pCPUs).
+### forward_smc (arm)
+> `= <boolean>`
+> Default: `false`
+If enabled, instead of trapping firmware SMC calls to Xen, allow SMC
+calls from VMs directly to the firmware. This option is UNSAFE and it is
+only meant for debugging. Systems with forward_smc=true are not security
 ### watchdog (x86)
 > `= force | <boolean>`
diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index e7384381cc..0580ac5762 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -95,11 +95,15 @@ static int __init parse_vwfi(const char *s)
 custom_param("vwfi", parse_vwfi);
+static bool forward_smc = false;
+boolean_param("forward_smc", forward_smc);
 register_t get_default_hcr_flags(void)
              (vwfi != NATIVE ? (HCR_TWI|HCR_TWE) : 0) |
+             (forward_smc ? 0 : HCR_TSC) |
 static enum {



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