[Xen-devel] [RFC 5/6] arm64: call enter_hypervisor_head only when it is needed

[Andrii Anisov <andrii.anisov@xxxxxxxxx>]

From: Andrii Anisov <andrii_anisov@xxxxxxxx>

On ARM64 we know exactly if trap happened from hypervisor or guest, so
we do not need to take that decision. This reduces a condition for
all enter_hypervisor_head calls and the function call for traps from
the hypervisor mode.

Currently, it is implemented for ARM64 only. Integrating the stuff
with ARM32 requires moving ` if ( guest_mode(regs) )` condition
into ARM32 specific traps.c

Signed-off-by: Andrii Anisov <andrii_anisov@xxxxxxxx>
---
 xen/arch/arm/arm64/entry.S |  6 ++--
 xen/arch/arm/traps.c       | 75 ++++++++++++++++++++++++----------------------
 2 files changed, 43 insertions(+), 38 deletions(-)

diff --git a/xen/arch/arm/arm64/entry.S b/xen/arch/arm/arm64/entry.S
index 8f28789..21c710d 100644
--- a/xen/arch/arm/arm64/entry.S
+++ b/xen/arch/arm/arm64/entry.S
@@ -211,7 +211,7 @@ hyp_irq:
         entry   hyp=1
         msr     daifclr, #4
         mov     x0, sp
-        bl      do_trap_irq
+        bl      do_trap_hyp_irq
         exit    hyp=1
 
 guest_sync:
@@ -321,7 +321,7 @@ guest_irq:
                     SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT)
         msr     daifclr, #4
         mov     x0, sp
-        bl      do_trap_irq
+        bl      do_trap_guest_irq
 1:
         exit    hyp=0, compat=0
 
@@ -364,7 +364,7 @@ guest_irq_compat:
                     SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT)
         msr     daifclr, #4
         mov     x0, sp
-        bl      do_trap_irq
+        bl      do_trap_guest_irq
 1:
         exit    hyp=0, compat=1
 
diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 5a9dc66..13726db 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -2011,48 +2011,45 @@ static inline bool needs_ssbd_flip(struct vcpu *v)
              cpu_require_ssbd_mitigation();
 }
 
-static void enter_hypervisor_head(struct cpu_user_regs *regs)
+static void enter_hypervisor_head(void)
 {
-    if ( guest_mode(regs) )
-    {
-        struct vcpu *v = current;
+    struct vcpu *v = current;
 
-        ASSERT(!local_irq_is_enabled());
+    ASSERT(!local_irq_is_enabled());
 
-        /* If the guest has disabled the workaround, bring it back on. */
-        if ( needs_ssbd_flip(v) )
-            arm_smccc_1_1_smc(ARM_SMCCC_ARCH_WORKAROUND_2_FID, 1, NULL);
+    /* If the guest has disabled the workaround, bring it back on. */
+    if ( needs_ssbd_flip(v) )
+        arm_smccc_1_1_smc(ARM_SMCCC_ARCH_WORKAROUND_2_FID, 1, NULL);
 
-        /*
-         * 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 ( v->arch.hcr_el2 & HCR_VA )
-            v->arch.hcr_el2 = READ_SYSREG(HCR_EL2);
+    /*
+     * 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 ( v->arch.hcr_el2 & HCR_VA )
+        v->arch.hcr_el2 = READ_SYSREG(HCR_EL2);
 
 #ifdef CONFIG_NEW_VGIC
-        /*
-         * We need to update the state of our emulated devices using level
-         * triggered interrupts before syncing back the VGIC state.
-         *
-         * TODO: Investigate whether this is necessary to do on every
-         * trap and how it can be optimised.
-         */
-        vtimer_update_irqs(v);
-        vcpu_update_evtchn_irq(v);
+    /*
+     * We need to update the state of our emulated devices using level
+     * triggered interrupts before syncing back the VGIC state.
+     *
+     * TODO: Investigate whether this is necessary to do on every
+     * trap and how it can be optimised.
+     */
+    vtimer_update_irqs(v);
+    vcpu_update_evtchn_irq(v);
 #endif
 
-        vgic_sync_from_lrs(v);
-    }
+    vgic_sync_from_lrs(v);
 }
 
 void do_trap_guest_sync(struct cpu_user_regs *regs)
 {
     const union hsr hsr = { .bits = regs->hsr };
 
-    enter_hypervisor_head(regs);
+    enter_hypervisor_head();
     local_irq_enable();
 
     switch ( hsr.ec )
@@ -2188,7 +2185,6 @@ void do_trap_hyp_sync(struct cpu_user_regs *regs)
 {
     const union hsr hsr = { .bits = regs->hsr };
 
-    enter_hypervisor_head(regs);
     local_irq_enable();
 
     switch ( hsr.ec )
@@ -2227,7 +2223,6 @@ void do_trap_hyp_sync(struct cpu_user_regs *regs)
 
 void do_trap_hyp_serror(struct cpu_user_regs *regs)
 {
-    enter_hypervisor_head(regs);
     local_irq_enable();
 
     __do_trap_serror(regs, VABORT_GEN_BY_GUEST(regs));
@@ -2235,21 +2230,31 @@ void do_trap_hyp_serror(struct cpu_user_regs *regs)
 
 void do_trap_guest_serror(struct cpu_user_regs *regs)
 {
-    enter_hypervisor_head(regs);
+    enter_hypervisor_head();
     local_irq_enable();
 
     __do_trap_serror(regs, true);
 }
 
-void do_trap_irq(struct cpu_user_regs *regs)
+void do_trap_guest_irq(struct cpu_user_regs *regs)
+{
+    enter_hypervisor_head();
+    gic_interrupt(regs, 0);
+}
+
+void do_trap_guest_fiq(struct cpu_user_regs *regs)
+{
+    enter_hypervisor_head();
+    gic_interrupt(regs, 1);
+}
+
+void do_trap_hyp_irq(struct cpu_user_regs *regs)
 {
-    enter_hypervisor_head(regs);
     gic_interrupt(regs, 0);
 }
 
-void do_trap_fiq(struct cpu_user_regs *regs)
+void do_trap_hyp_fiq(struct cpu_user_regs *regs)
 {
-    enter_hypervisor_head(regs);
     gic_interrupt(regs, 1);
 }
 
-- 
2.7.4


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