[Xen-devel] [PATCH 04/18] xen/arm: Save HCR_EL2 when a guest took the SError

[Wei Chen <Wei.Chen@xxxxxxx>]

The HCR_EL2.VSE (HCR.VA for aarch32) bit can be used to generate a
virtual abort to guest. The HCR_EL2.VSE bit has a peculiar feature
of getting cleared when the guest has taken the abort (this is the
only bit that behaves as such in HCR_EL2 register).

This means that if we set the HCR_EL2.VSE bit to signal such an abort,
we must preserve it in the guest context until it disappears from
HCR_EL2, and at which point it must be cleared from the context. This
is achieved by reading back from HCR_EL2 until the guest takes the
fault.

If we preserved a pending VSE in guest context, we have to restore
it to HCR_EL2 when context switch to this guest. This is achieved
by writing saved HCR_EL2 value in guest context back to HCR_EL2
register before return to guest. This had been done by the patch
of "Restore HCR_EL2 register".

Signed-off-by: Wei Chen <Wei.Chen@xxxxxxx>
---
 xen/arch/arm/traps.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 9792d02..476e2be 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -2641,7 +2641,18 @@ static void do_trap_smc(struct cpu_user_regs *regs, 
const union hsr hsr)
 static void enter_hypervisor_head(struct cpu_user_regs *regs)
 {
     if ( guest_mode(regs) )
+    {
+        /*
+         * If we pended a virtual abort, preserve it until it gets cleared.
+         * See ARM ARM DDI 0487A.j D1.14.3 (Virtual Interrupts) for details,
+         * but the crucial bit is "On taking a vSError interrupt, HCR_EL2.VSE
+         * (alias of HCR.VA) is cleared to 0."
+         */
+        if ( current->arch.hcr_el2 & HCR_VA )
+            current->arch.hcr_el2 = READ_SYSREG(HCR_EL2);
+
         gic_clear_lrs(current);
+    }
 }
 
 asmlinkage void do_trap_hypervisor(struct cpu_user_regs *regs)
-- 
2.7.4


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