[Xen-devel] [PATCH for-4.13 v4 09/19] xen/arm: traps: Rework entry/exit from the guest path

[Julien Grall <julien.grall@xxxxxxx>]

At the moment, enter_hypervisor_head() and leave_hypervisor_tail() are
used to deal with actions to be done before/after any guest request is
handled.

While they are meant to work in pair, the former is called for most of
the traps, including traps from the same exception level (i.e.
hypervisor) whilst the latter will only be called when returning to the
guest.

As pointed out, the enter_hypervisor_head() is not called from all the
traps, so this makes potentially difficult to extend it for the dealing
with same exception level.

Furthermore, some assembly only path will require to call
enter_hypervisor_tail(). So the function is now directly call by
assembly in for guest vector only. This means that the check whether we
are called in a guest trap can now be removed.

Take the opportunity to rename enter_hypervisor_tail() and
leave_hypervisor_tail() to something more meaningful and document them.
This should help everyone to understand the purpose of the two
functions.

Note that enter_hypervisor_tail() does not take any parameters anymore
as after the rework, the code does not use them anymore.

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

---
    Changes in v4:
        - Add Stefano's acked-by

    Changes in v3:
        - Update the documentation on the callee side of
        leave_hypervisor_to_guest().
        - Replace "interrupts" with "IRQ"

    Changes in v2:
        - Update in-code comment
        - Remove 'regs' parameter from enter_hypervisor_tail()
        - Add arm32 code
---
 xen/arch/arm/arm32/entry.S |  5 +++-
 xen/arch/arm/arm64/entry.S |  3 +-
 xen/arch/arm/traps.c       | 71 ++++++++++++++++++++++------------------------
 3 files changed, 40 insertions(+), 39 deletions(-)

diff --git a/xen/arch/arm/arm32/entry.S b/xen/arch/arm/arm32/entry.S
index ec90cca093..5abff24e91 100644
--- a/xen/arch/arm/arm32/entry.S
+++ b/xen/arch/arm/arm32/entry.S
@@ -177,6 +177,9 @@ skip_check:
         .if     \guest_iflags != n
         cpsie   \guest_iflags
         .endif
+
+        bl      enter_hypervisor_from_guest
+
 2:
         /* We are ready to handle the trap, setup the registers and jump. */
         adr     lr, return_from_trap
@@ -332,7 +335,7 @@ ENTRY(return_to_new_vcpu32)
 return_to_guest:
         mov r11, sp
         bic sp, #7 /* Align the stack pointer */
-        bl leave_hypervisor_tail /* Disables interrupts on return */
+        bl leave_hypervisor_to_guest /* Mask IRQ on return */
         mov sp, r11
         RESTORE_ONE_BANKED(SP_usr)
         /* LR_usr is the same physical register as lr and is restored below */
diff --git a/xen/arch/arm/arm64/entry.S b/xen/arch/arm/arm64/entry.S
index d94c13e7bf..97dc60210d 100644
--- a/xen/arch/arm/arm64/entry.S
+++ b/xen/arch/arm/arm64/entry.S
@@ -165,7 +165,7 @@
 
         .if \hyp == 0         /* Guest mode */
 
-        bl      leave_hypervisor_tail /* Disables interrupts on return */
+        bl      leave_hypervisor_to_guest /* Mask IRQ on return */
 
         exit_guest \compat
 
@@ -192,6 +192,7 @@
                     "nop; nop",
                     SKIP_SYNCHRONIZE_SERROR_ENTRY_EXIT)
         msr     daifclr, \iflags
+        bl      enter_hypervisor_from_guest
         mov     x0, sp
         bl      do_trap_\trap
 1:
diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 12c52a3860..adbedc2d15 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -1984,47 +1984,46 @@ static inline bool needs_ssbd_flip(struct vcpu *v)
              cpu_require_ssbd_mitigation();
 }
 
-static void enter_hypervisor_head(struct cpu_user_regs *regs)
+/*
+ * Actions that needs to be done after entering the hypervisor from the
+ * guest and before we handle any request.
+ */
+void enter_hypervisor_from_guest(void)
 {
-    if ( guest_mode(regs) )
-    {
-        struct vcpu *v = current;
+    struct vcpu *v = current;
 
-        /* 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);
-
     switch ( hsr.ec )
     {
     case HSR_EC_WFI_WFE:
@@ -2158,8 +2157,6 @@ void do_trap_hyp_sync(struct cpu_user_regs *regs)
 {
     const union hsr hsr = { .bits = regs->hsr };
 
-    enter_hypervisor_head(regs);
-
     switch ( hsr.ec )
     {
 #ifdef CONFIG_ARM_64
@@ -2196,27 +2193,21 @@ void do_trap_hyp_sync(struct cpu_user_regs *regs)
 
 void do_trap_hyp_serror(struct cpu_user_regs *regs)
 {
-    enter_hypervisor_head(regs);
-
     __do_trap_serror(regs, VABORT_GEN_BY_GUEST(regs));
 }
 
 void do_trap_guest_serror(struct cpu_user_regs *regs)
 {
-    enter_hypervisor_head(regs);
-
     __do_trap_serror(regs, true);
 }
 
 void do_trap_irq(struct cpu_user_regs *regs)
 {
-    enter_hypervisor_head(regs);
     gic_interrupt(regs, 0);
 }
 
 void do_trap_fiq(struct cpu_user_regs *regs)
 {
-    enter_hypervisor_head(regs);
     gic_interrupt(regs, 1);
 }
 
@@ -2259,7 +2250,13 @@ static void check_for_vcpu_work(void)
     local_irq_disable();
 }
 
-void leave_hypervisor_tail(void)
+/*
+ * Actions that needs to be done before entering the guest. This is the
+ * last thing executed before the guest context is fully restored.
+ *
+ * The function will return with IRQ masked.
+ */
+void leave_hypervisor_to_guest(void)
 {
     local_irq_disable();
 
-- 
2.11.0


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