[PATCH v3 0/2] x86/xen: simplify irq pvops

[PATCH v3 0/2] x86/xen: simplify irq pvops

[Juergen Gross]

The pvops function for Xen PV guests handling the interrupt flag are
much more complex than needed.

With the supported Xen hypervisor versions they can be simplified a
lot, especially by removing the need for disabling preemption.

Juergen Gross (2):
  x86/xen: remove xen_have_vcpu_info_placement flag
  x86/xen: switch initial pvops IRQ functions to dummy ones

 arch/x86/include/asm/paravirt_types.h |   2 +
 arch/x86/kernel/paravirt.c            |  13 ++-
 arch/x86/xen/enlighten.c              | 116 ++++++--------------------
 arch/x86/xen/enlighten_hvm.c          |   6 +-
 arch/x86/xen/enlighten_pv.c           |  28 ++-----
 arch/x86/xen/irq.c                    |  61 +-------------
 arch/x86/xen/smp.c                    |  24 ------
 arch/x86/xen/xen-ops.h                |   4 +-
 8 files changed, 53 insertions(+), 201 deletions(-)

-- 
2.26.2

[PATCH v3 0/2] x86/xen: simplify irq pvops

[Juergen Gross via Virtualization]

The pvops function for Xen PV guests handling the interrupt flag are
much more complex than needed.

With the supported Xen hypervisor versions they can be simplified a
lot, especially by removing the need for disabling preemption.

Juergen Gross (2):
  x86/xen: remove xen_have_vcpu_info_placement flag
  x86/xen: switch initial pvops IRQ functions to dummy ones

 arch/x86/include/asm/paravirt_types.h |   2 +
 arch/x86/kernel/paravirt.c            |  13 ++-
 arch/x86/xen/enlighten.c              | 116 ++++++--------------------
 arch/x86/xen/enlighten_hvm.c          |   6 +-
 arch/x86/xen/enlighten_pv.c           |  28 ++-----
 arch/x86/xen/irq.c                    |  61 +-------------
 arch/x86/xen/smp.c                    |  24 ------
 arch/x86/xen/xen-ops.h                |   4 +-
 8 files changed, 53 insertions(+), 201 deletions(-)

-- 
2.26.2

_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
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[PATCH v3 1/2] x86/xen: remove xen_have_vcpu_info_placement flag

[Juergen Gross]

The flag xen_have_vcpu_info_placement was needed to support Xen
hypervisors older than version 3.4, which didn't support the
VCPUOP_register_vcpu_info hypercall. Today the Linux kernel requires
at least Xen 4.0 to be able to run, so xen_have_vcpu_info_placement
can be dropped (in theory the flag was used to ensure a working kernel
even in case of the VCPUOP_register_vcpu_info hypercall failing for
other reasons than the hypercall not being supported, but the only
cases covered by the flag would be parameter errors, which ought not
to be made anyway).

This allows to let some functions return void now, as they can never
fail.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
 arch/x86/xen/enlighten.c     | 97 +++++++++---------------------------
 arch/x86/xen/enlighten_hvm.c |  6 +--
 arch/x86/xen/enlighten_pv.c  | 28 ++---------
 arch/x86/xen/smp.c           | 24 ---------
 arch/x86/xen/xen-ops.h       |  4 +-
 5 files changed, 33 insertions(+), 126 deletions(-)

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 95d970359e17..006b4a814fac 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -84,21 +84,6 @@ EXPORT_SYMBOL(xen_start_flags);
  */
 struct shared_info *HYPERVISOR_shared_info = &xen_dummy_shared_info;
 
-/*
- * Flag to determine whether vcpu info placement is available on all
- * VCPUs.  We assume it is to start with, and then set it to zero on
- * the first failure.  This is because it can succeed on some VCPUs
- * and not others, since it can involve hypervisor memory allocation,
- * or because the guest failed to guarantee all the appropriate
- * constraints on all VCPUs (ie buffer can't cross a page boundary).
- *
- * Note that any particular CPU may be using a placed vcpu structure,
- * but we can only optimise if the all are.
- *
- * 0: not available, 1: available
- */
-int xen_have_vcpu_info_placement = 1;
-
 static int xen_cpu_up_online(unsigned int cpu)
 {
 	xen_init_lock_cpu(cpu);
@@ -124,10 +109,8 @@ int xen_cpuhp_setup(int (*cpu_up_prepare_cb)(unsigned int),
 	return rc >= 0 ? 0 : rc;
 }
 
-static int xen_vcpu_setup_restore(int cpu)
+static void xen_vcpu_setup_restore(int cpu)
 {
-	int rc = 0;
-
 	/* Any per_cpu(xen_vcpu) is stale, so reset it */
 	xen_vcpu_info_reset(cpu);
 
@@ -136,11 +119,8 @@ static int xen_vcpu_setup_restore(int cpu)
 	 * be handled by hotplug.
 	 */
 	if (xen_pv_domain() ||
-	    (xen_hvm_domain() && cpu_online(cpu))) {
-		rc = xen_vcpu_setup(cpu);
-	}
-
-	return rc;
+	    (xen_hvm_domain() && cpu_online(cpu)))
+		xen_vcpu_setup(cpu);
 }
 
 /*
@@ -150,7 +130,7 @@ static int xen_vcpu_setup_restore(int cpu)
  */
 void xen_vcpu_restore(void)
 {
-	int cpu, rc;
+	int cpu;
 
 	for_each_possible_cpu(cpu) {
 		bool other_cpu = (cpu != smp_processor_id());
@@ -170,20 +150,9 @@ void xen_vcpu_restore(void)
 		if (xen_pv_domain() || xen_feature(XENFEAT_hvm_safe_pvclock))
 			xen_setup_runstate_info(cpu);
 
-		rc = xen_vcpu_setup_restore(cpu);
-		if (rc)
-			pr_emerg_once("vcpu restore failed for cpu=%d err=%d. "
-					"System will hang.\n", cpu, rc);
-		/*
-		 * In case xen_vcpu_setup_restore() fails, do not bring up the
-		 * VCPU. This helps us avoid the resulting OOPS when the VCPU
-		 * accesses pvclock_vcpu_time via xen_vcpu (which is NULL.)
-		 * Note that this does not improve the situation much -- now the
-		 * VM hangs instead of OOPSing -- with the VCPUs that did not
-		 * fail, spinning in stop_machine(), waiting for the failed
-		 * VCPUs to come up.
-		 */
-		if (other_cpu && is_up && (rc == 0) &&
+		xen_vcpu_setup_restore(cpu);
+
+		if (other_cpu && is_up &&
 		    HYPERVISOR_vcpu_op(VCPUOP_up, xen_vcpu_nr(cpu), NULL))
 			BUG();
 	}
@@ -200,7 +169,7 @@ void xen_vcpu_info_reset(int cpu)
 	}
 }
 
-int xen_vcpu_setup(int cpu)
+void xen_vcpu_setup(int cpu)
 {
 	struct vcpu_register_vcpu_info info;
 	int err;
@@ -221,44 +190,26 @@ int xen_vcpu_setup(int cpu)
 	 */
 	if (xen_hvm_domain()) {
 		if (per_cpu(xen_vcpu, cpu) == &per_cpu(xen_vcpu_info, cpu))
-			return 0;
+			return;
 	}
 
-	if (xen_have_vcpu_info_placement) {
-		vcpup = &per_cpu(xen_vcpu_info, cpu);
-		info.mfn = arbitrary_virt_to_mfn(vcpup);
-		info.offset = offset_in_page(vcpup);
+	vcpup = &per_cpu(xen_vcpu_info, cpu);
+	info.mfn = arbitrary_virt_to_mfn(vcpup);
+	info.offset = offset_in_page(vcpup);
 
-		/*
-		 * Check to see if the hypervisor will put the vcpu_info
-		 * structure where we want it, which allows direct access via
-		 * a percpu-variable.
-		 * N.B. This hypercall can _only_ be called once per CPU.
-		 * Subsequent calls will error out with -EINVAL. This is due to
-		 * the fact that hypervisor has no unregister variant and this
-		 * hypercall does not allow to over-write info.mfn and
-		 * info.offset.
-		 */
-		err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info,
-					 xen_vcpu_nr(cpu), &info);
-
-		if (err) {
-			pr_warn_once("register_vcpu_info failed: cpu=%d err=%d\n",
-				     cpu, err);
-			xen_have_vcpu_info_placement = 0;
-		} else {
-			/*
-			 * This cpu is using the registered vcpu info, even if
-			 * later ones fail to.
-			 */
-			per_cpu(xen_vcpu, cpu) = vcpup;
-		}
-	}
-
-	if (!xen_have_vcpu_info_placement)
-		xen_vcpu_info_reset(cpu);
+	/*
+	 * N.B. This hypercall can _only_ be called once per CPU.
+	 * Subsequent calls will error out with -EINVAL. This is due to
+	 * the fact that hypervisor has no unregister variant and this
+	 * hypercall does not allow to over-write info.mfn and
+	 * info.offset.
+	 */
+	err = HYPERVISOR_vcpu_op(VCPUOP_register_vcpu_info, xen_vcpu_nr(cpu),
+				 &info);
+	if (err)
+		panic("register_vcpu_info failed: cpu=%d err=%d\n", cpu, err);
 
-	return ((per_cpu(xen_vcpu, cpu) == NULL) ? -ENODEV : 0);
+	per_cpu(xen_vcpu, cpu) = vcpup;
 }
 
 void __init xen_banner(void)
diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index e68ea5f4ad1c..42300941ec29 100644
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -163,9 +163,9 @@ static int xen_cpu_up_prepare_hvm(unsigned int cpu)
 		per_cpu(xen_vcpu_id, cpu) = cpu_acpi_id(cpu);
 	else
 		per_cpu(xen_vcpu_id, cpu) = cpu;
-	rc = xen_vcpu_setup(cpu);
-	if (rc || !xen_have_vector_callback)
-		return rc;
+	xen_vcpu_setup(cpu);
+	if (!xen_have_vector_callback)
+		return 0;
 
 	if (xen_feature(XENFEAT_hvm_safe_pvclock))
 		xen_setup_timer(cpu);
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index a7b7d674f500..2635a00be42d 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -993,31 +993,13 @@ void __init xen_setup_vcpu_info_placement(void)
 	for_each_possible_cpu(cpu) {
 		/* Set up direct vCPU id mapping for PV guests. */
 		per_cpu(xen_vcpu_id, cpu) = cpu;
-
-		/*
-		 * xen_vcpu_setup(cpu) can fail  -- in which case it
-		 * falls back to the shared_info version for cpus
-		 * where xen_vcpu_nr(cpu) < MAX_VIRT_CPUS.
-		 *
-		 * xen_cpu_up_prepare_pv() handles the rest by failing
-		 * them in hotplug.
-		 */
-		(void) xen_vcpu_setup(cpu);
+		xen_vcpu_setup(cpu);
 	}
 
-	/*
-	 * xen_vcpu_setup managed to place the vcpu_info within the
-	 * percpu area for all cpus, so make use of it.
-	 */
-	if (xen_have_vcpu_info_placement) {
-		pv_ops.irq.save_fl = __PV_IS_CALLEE_SAVE(xen_save_fl_direct);
-		pv_ops.irq.irq_disable =
-			__PV_IS_CALLEE_SAVE(xen_irq_disable_direct);
-		pv_ops.irq.irq_enable =
-			__PV_IS_CALLEE_SAVE(xen_irq_enable_direct);
-		pv_ops.mmu.read_cr2 =
-			__PV_IS_CALLEE_SAVE(xen_read_cr2_direct);
-	}
+	pv_ops.irq.save_fl = __PV_IS_CALLEE_SAVE(xen_save_fl_direct);
+	pv_ops.irq.irq_disable = __PV_IS_CALLEE_SAVE(xen_irq_disable_direct);
+	pv_ops.irq.irq_enable = __PV_IS_CALLEE_SAVE(xen_irq_enable_direct);
+	pv_ops.mmu.read_cr2 = __PV_IS_CALLEE_SAVE(xen_read_cr2_direct);
 }
 
 static const struct pv_info xen_info __initconst = {
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index c1b2f764b29a..bafa61b1482f 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -121,34 +121,10 @@ int xen_smp_intr_init(unsigned int cpu)
 
 void __init xen_smp_cpus_done(unsigned int max_cpus)
 {
-	int cpu, rc, count = 0;
-
 	if (xen_hvm_domain())
 		native_smp_cpus_done(max_cpus);
 	else
 		calculate_max_logical_packages();
-
-	if (xen_have_vcpu_info_placement)
-		return;
-
-	for_each_online_cpu(cpu) {
-		if (xen_vcpu_nr(cpu) < MAX_VIRT_CPUS)
-			continue;
-
-		rc = remove_cpu(cpu);
-
-		if (rc == 0) {
-			/*
-			 * Reset vcpu_info so this cpu cannot be onlined again.
-			 */
-			xen_vcpu_info_reset(cpu);
-			count++;
-		} else {
-			pr_warn("%s: failed to bring CPU %d down, error %d\n",
-				__func__, cpu, rc);
-		}
-	}
-	WARN(count, "%s: brought %d CPUs offline\n", __func__, count);
 }
 
 void xen_smp_send_reschedule(int cpu)
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 8bc8b72a205d..fd0fec6e92f4 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -76,9 +76,7 @@ irqreturn_t xen_debug_interrupt(int irq, void *dev_id);
 
 bool xen_vcpu_stolen(int vcpu);
 
-extern int xen_have_vcpu_info_placement;
-
-int xen_vcpu_setup(int cpu);
+void xen_vcpu_setup(int cpu);
 void xen_vcpu_info_reset(int cpu);
 void xen_setup_vcpu_info_placement(void);
 
-- 
2.26.2

[PATCH v3 2/2] x86/xen: switch initial pvops IRQ functions to dummy ones

[Juergen Gross]

The initial pvops functions handling irq flags will only ever be called
before interrupts are being enabled.

So switch them to be dummy functions:
- xen_save_fl() can always return 0
- xen_irq_disable() is a nop
- xen_irq_enable() can BUG()

Add some generic paravirt functions for that purpose.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
V3:
- make paravirt_BUG() noinstr
---
 arch/x86/include/asm/paravirt_types.h |  2 +
 arch/x86/kernel/paravirt.c            | 13 +++++-
 arch/x86/xen/enlighten.c              | 19 +--------
 arch/x86/xen/irq.c                    | 61 ++-------------------------
 4 files changed, 20 insertions(+), 75 deletions(-)

diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index d9d6b0203ec4..fc1151e77569 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -577,7 +577,9 @@ void paravirt_leave_lazy_mmu(void);
 void paravirt_flush_lazy_mmu(void);
 
 void _paravirt_nop(void);
+void paravirt_BUG(void);
 u64 _paravirt_ident_64(u64);
+unsigned long paravirt_ret0(void);
 
 #define paravirt_nop	((void *)_paravirt_nop)
 
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 04cafc057bed..b44814dfe83f 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -46,6 +46,17 @@ asm (".pushsection .entry.text, \"ax\"\n"
      ".type _paravirt_nop, @function\n\t"
      ".popsection");
 
+/* stub always returning 0. */
+asm (".pushsection .entry.text, \"ax\"\n"
+     ".global paravirt_ret0\n"
+     "paravirt_ret0:\n\t"
+     "xor %" _ASM_AX ", %" _ASM_AX ";\n\t"
+     "ret\n\t"
+     ".size paravirt_ret0, . - paravirt_ret0\n\t"
+     ".type paravirt_ret0, @function\n\t"
+     ".popsection");
+
+
 void __init default_banner(void)
 {
 	printk(KERN_INFO "Booting paravirtualized kernel on %s\n",
@@ -53,7 +64,7 @@ void __init default_banner(void)
 }
 
 /* Undefined instruction for dealing with missing ops pointers. */
-static void paravirt_BUG(void)
+noinstr void paravirt_BUG(void)
 {
 	BUG();
 }
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 006b4a814fac..30c6e986a6cd 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -31,25 +31,10 @@ EXPORT_SYMBOL_GPL(hypercall_page);
  * Pointer to the xen_vcpu_info structure or
  * &HYPERVISOR_shared_info->vcpu_info[cpu]. See xen_hvm_init_shared_info
  * and xen_vcpu_setup for details. By default it points to share_info->vcpu_info
- * but if the hypervisor supports VCPUOP_register_vcpu_info then it can point
- * to xen_vcpu_info. The pointer is used in __xen_evtchn_do_upcall to
- * acknowledge pending events.
- * Also more subtly it is used by the patched version of irq enable/disable
- * e.g. xen_irq_enable_direct and xen_iret in PV mode.
- *
- * The desire to be able to do those mask/unmask operations as a single
- * instruction by using the per-cpu offset held in %gs is the real reason
- * vcpu info is in a per-cpu pointer and the original reason for this
- * hypercall.
- *
+ * but during boot it is switched to point to xen_vcpu_info.
+ * The pointer is used in __xen_evtchn_do_upcall to acknowledge pending events.
  */
 DEFINE_PER_CPU(struct vcpu_info *, xen_vcpu);
-
-/*
- * Per CPU pages used if hypervisor supports VCPUOP_register_vcpu_info
- * hypercall. This can be used both in PV and PVHVM mode. The structure
- * overrides the default per_cpu(xen_vcpu, cpu) value.
- */
 DEFINE_PER_CPU(struct vcpu_info, xen_vcpu_info);
 
 /* Linux <-> Xen vCPU id mapping */
diff --git a/arch/x86/xen/irq.c b/arch/x86/xen/irq.c
index dfa091d79c2e..ae8537583102 100644
--- a/arch/x86/xen/irq.c
+++ b/arch/x86/xen/irq.c
@@ -24,60 +24,6 @@ void xen_force_evtchn_callback(void)
 	(void)HYPERVISOR_xen_version(0, NULL);
 }
 
-asmlinkage __visible unsigned long xen_save_fl(void)
-{
-	struct vcpu_info *vcpu;
-	unsigned long flags;
-
-	vcpu = this_cpu_read(xen_vcpu);
-
-	/* flag has opposite sense of mask */
-	flags = !vcpu->evtchn_upcall_mask;
-
-	/* convert to IF type flag
-	   -0 -> 0x00000000
-	   -1 -> 0xffffffff
-	*/
-	return (-flags) & X86_EFLAGS_IF;
-}
-PV_CALLEE_SAVE_REGS_THUNK(xen_save_fl);
-
-asmlinkage __visible void xen_irq_disable(void)
-{
-	/* There's a one instruction preempt window here.  We need to
-	   make sure we're don't switch CPUs between getting the vcpu
-	   pointer and updating the mask. */
-	preempt_disable();
-	this_cpu_read(xen_vcpu)->evtchn_upcall_mask = 1;
-	preempt_enable_no_resched();
-}
-PV_CALLEE_SAVE_REGS_THUNK(xen_irq_disable);
-
-asmlinkage __visible void xen_irq_enable(void)
-{
-	struct vcpu_info *vcpu;
-
-	/*
-	 * We may be preempted as soon as vcpu->evtchn_upcall_mask is
-	 * cleared, so disable preemption to ensure we check for
-	 * events on the VCPU we are still running on.
-	 */
-	preempt_disable();
-
-	vcpu = this_cpu_read(xen_vcpu);
-	vcpu->evtchn_upcall_mask = 0;
-
-	/* Doesn't matter if we get preempted here, because any
-	   pending event will get dealt with anyway. */
-
-	barrier(); /* unmask then check (avoid races) */
-	if (unlikely(vcpu->evtchn_upcall_pending))
-		xen_force_evtchn_callback();
-
-	preempt_enable();
-}
-PV_CALLEE_SAVE_REGS_THUNK(xen_irq_enable);
-
 static void xen_safe_halt(void)
 {
 	/* Blocking includes an implicit local_irq_enable(). */
@@ -95,9 +41,10 @@ static void xen_halt(void)
 }
 
 static const struct pv_irq_ops xen_irq_ops __initconst = {
-	.save_fl = PV_CALLEE_SAVE(xen_save_fl),
-	.irq_disable = PV_CALLEE_SAVE(xen_irq_disable),
-	.irq_enable = PV_CALLEE_SAVE(xen_irq_enable),
+	/* Initial interrupt flag handling only called while interrupts off. */
+	.save_fl = __PV_IS_CALLEE_SAVE(paravirt_ret0),
+	.irq_disable = __PV_IS_CALLEE_SAVE(paravirt_nop),
+	.irq_enable = __PV_IS_CALLEE_SAVE(paravirt_BUG),
 
 	.safe_halt = xen_safe_halt,
 	.halt = xen_halt,
-- 
2.26.2

[PATCH v3 2/2] x86/xen: switch initial pvops IRQ functions to dummy ones

[Juergen Gross via Virtualization]

The initial pvops functions handling irq flags will only ever be called
before interrupts are being enabled.

So switch them to be dummy functions:
- xen_save_fl() can always return 0
- xen_irq_disable() is a nop
- xen_irq_enable() can BUG()

Add some generic paravirt functions for that purpose.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
---
V3:
- make paravirt_BUG() noinstr
---
 arch/x86/include/asm/paravirt_types.h |  2 +
 arch/x86/kernel/paravirt.c            | 13 +++++-
 arch/x86/xen/enlighten.c              | 19 +--------
 arch/x86/xen/irq.c                    | 61 ++-------------------------
 4 files changed, 20 insertions(+), 75 deletions(-)

diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index d9d6b0203ec4..fc1151e77569 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -577,7 +577,9 @@ void paravirt_leave_lazy_mmu(void);
 void paravirt_flush_lazy_mmu(void);
 
 void _paravirt_nop(void);
+void paravirt_BUG(void);
 u64 _paravirt_ident_64(u64);
+unsigned long paravirt_ret0(void);
 
 #define paravirt_nop	((void *)_paravirt_nop)
 
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index 04cafc057bed..b44814dfe83f 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -46,6 +46,17 @@ asm (".pushsection .entry.text, \"ax\"\n"
      ".type _paravirt_nop, @function\n\t"
      ".popsection");
 
+/* stub always returning 0. */
+asm (".pushsection .entry.text, \"ax\"\n"
+     ".global paravirt_ret0\n"
+     "paravirt_ret0:\n\t"
+     "xor %" _ASM_AX ", %" _ASM_AX ";\n\t"
+     "ret\n\t"
+     ".size paravirt_ret0, . - paravirt_ret0\n\t"
+     ".type paravirt_ret0, @function\n\t"
+     ".popsection");
+
+
 void __init default_banner(void)
 {
 	printk(KERN_INFO "Booting paravirtualized kernel on %s\n",
@@ -53,7 +64,7 @@ void __init default_banner(void)
 }
 
 /* Undefined instruction for dealing with missing ops pointers. */
-static void paravirt_BUG(void)
+noinstr void paravirt_BUG(void)
 {
 	BUG();
 }
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 006b4a814fac..30c6e986a6cd 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -31,25 +31,10 @@ EXPORT_SYMBOL_GPL(hypercall_page);
  * Pointer to the xen_vcpu_info structure or
  * &HYPERVISOR_shared_info->vcpu_info[cpu]. See xen_hvm_init_shared_info
  * and xen_vcpu_setup for details. By default it points to share_info->vcpu_info
- * but if the hypervisor supports VCPUOP_register_vcpu_info then it can point
- * to xen_vcpu_info. The pointer is used in __xen_evtchn_do_upcall to
- * acknowledge pending events.
- * Also more subtly it is used by the patched version of irq enable/disable
- * e.g. xen_irq_enable_direct and xen_iret in PV mode.
- *
- * The desire to be able to do those mask/unmask operations as a single
- * instruction by using the per-cpu offset held in %gs is the real reason
- * vcpu info is in a per-cpu pointer and the original reason for this
- * hypercall.
- *
+ * but during boot it is switched to point to xen_vcpu_info.
+ * The pointer is used in __xen_evtchn_do_upcall to acknowledge pending events.
  */
 DEFINE_PER_CPU(struct vcpu_info *, xen_vcpu);
-
-/*
- * Per CPU pages used if hypervisor supports VCPUOP_register_vcpu_info
- * hypercall. This can be used both in PV and PVHVM mode. The structure
- * overrides the default per_cpu(xen_vcpu, cpu) value.
- */
 DEFINE_PER_CPU(struct vcpu_info, xen_vcpu_info);
 
 /* Linux <-> Xen vCPU id mapping */
diff --git a/arch/x86/xen/irq.c b/arch/x86/xen/irq.c
index dfa091d79c2e..ae8537583102 100644
--- a/arch/x86/xen/irq.c
+++ b/arch/x86/xen/irq.c
@@ -24,60 +24,6 @@ void xen_force_evtchn_callback(void)
 	(void)HYPERVISOR_xen_version(0, NULL);
 }
 
-asmlinkage __visible unsigned long xen_save_fl(void)
-{
-	struct vcpu_info *vcpu;
-	unsigned long flags;
-
-	vcpu = this_cpu_read(xen_vcpu);
-
-	/* flag has opposite sense of mask */
-	flags = !vcpu->evtchn_upcall_mask;
-
-	/* convert to IF type flag
-	   -0 -> 0x00000000
-	   -1 -> 0xffffffff
-	*/
-	return (-flags) & X86_EFLAGS_IF;
-}
-PV_CALLEE_SAVE_REGS_THUNK(xen_save_fl);
-
-asmlinkage __visible void xen_irq_disable(void)
-{
-	/* There's a one instruction preempt window here.  We need to
-	   make sure we're don't switch CPUs between getting the vcpu
-	   pointer and updating the mask. */
-	preempt_disable();
-	this_cpu_read(xen_vcpu)->evtchn_upcall_mask = 1;
-	preempt_enable_no_resched();
-}
-PV_CALLEE_SAVE_REGS_THUNK(xen_irq_disable);
-
-asmlinkage __visible void xen_irq_enable(void)
-{
-	struct vcpu_info *vcpu;
-
-	/*
-	 * We may be preempted as soon as vcpu->evtchn_upcall_mask is
-	 * cleared, so disable preemption to ensure we check for
-	 * events on the VCPU we are still running on.
-	 */
-	preempt_disable();
-
-	vcpu = this_cpu_read(xen_vcpu);
-	vcpu->evtchn_upcall_mask = 0;
-
-	/* Doesn't matter if we get preempted here, because any
-	   pending event will get dealt with anyway. */
-
-	barrier(); /* unmask then check (avoid races) */
-	if (unlikely(vcpu->evtchn_upcall_pending))
-		xen_force_evtchn_callback();
-
-	preempt_enable();
-}
-PV_CALLEE_SAVE_REGS_THUNK(xen_irq_enable);
-
 static void xen_safe_halt(void)
 {
 	/* Blocking includes an implicit local_irq_enable(). */
@@ -95,9 +41,10 @@ static void xen_halt(void)
 }
 
 static const struct pv_irq_ops xen_irq_ops __initconst = {
-	.save_fl = PV_CALLEE_SAVE(xen_save_fl),
-	.irq_disable = PV_CALLEE_SAVE(xen_irq_disable),
-	.irq_enable = PV_CALLEE_SAVE(xen_irq_enable),
+	/* Initial interrupt flag handling only called while interrupts off. */
+	.save_fl = __PV_IS_CALLEE_SAVE(paravirt_ret0),
+	.irq_disable = __PV_IS_CALLEE_SAVE(paravirt_nop),
+	.irq_enable = __PV_IS_CALLEE_SAVE(paravirt_BUG),
 
 	.safe_halt = xen_safe_halt,
 	.halt = xen_halt,
-- 
2.26.2

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Re: [PATCH v3 0/2] x86/xen: simplify irq pvops

[Boris Ostrovsky]

On 10/28/21 3:27 AM, Juergen Gross wrote:
> The pvops function for Xen PV guests handling the interrupt flag are
> much more complex than needed.
>
> With the supported Xen hypervisor versions they can be simplified a
> lot, especially by removing the need for disabling preemption.
>
> Juergen Gross (2):
>    x86/xen: remove xen_have_vcpu_info_placement flag
>    x86/xen: switch initial pvops IRQ functions to dummy ones
>
>   arch/x86/include/asm/paravirt_types.h |   2 +
>   arch/x86/kernel/paravirt.c            |  13 ++-
>   arch/x86/xen/enlighten.c              | 116 ++++++--------------------
>   arch/x86/xen/enlighten_hvm.c          |   6 +-
>   arch/x86/xen/enlighten_pv.c           |  28 ++-----
>   arch/x86/xen/irq.c                    |  61 +-------------
>   arch/x86/xen/smp.c                    |  24 ------
>   arch/x86/xen/xen-ops.h                |   4 +-
>   8 files changed, 53 insertions(+), 201 deletions(-)
>

Applied to for-linus-5.16


-boris

_______________________________________________
Virtualization mailing list
Virtualization@lists.linux-foundation.org
https://lists.linuxfoundation.org/mailman/listinfo/virtualization

Re: [PATCH v3 0/2] x86/xen: simplify irq pvops

[Boris Ostrovsky]

On 10/28/21 3:27 AM, Juergen Gross wrote:
> The pvops function for Xen PV guests handling the interrupt flag are
> much more complex than needed.
>
> With the supported Xen hypervisor versions they can be simplified a
> lot, especially by removing the need for disabling preemption.
>
> Juergen Gross (2):
>    x86/xen: remove xen_have_vcpu_info_placement flag
>    x86/xen: switch initial pvops IRQ functions to dummy ones
>
>   arch/x86/include/asm/paravirt_types.h |   2 +
>   arch/x86/kernel/paravirt.c            |  13 ++-
>   arch/x86/xen/enlighten.c              | 116 ++++++--------------------
>   arch/x86/xen/enlighten_hvm.c          |   6 +-
>   arch/x86/xen/enlighten_pv.c           |  28 ++-----
>   arch/x86/xen/irq.c                    |  61 +-------------
>   arch/x86/xen/smp.c                    |  24 ------
>   arch/x86/xen/xen-ops.h                |   4 +-
>   8 files changed, 53 insertions(+), 201 deletions(-)
>

Applied to for-linus-5.16


-boris