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Date: Tue, 28 Apr 2020 01:24:54 +0200
From: Thomas Gleixner <tglx@...utronix.de>
To: Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: x86@...nel.org, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
Juergen Gross <jgross@...e.com>
Subject: Re: [PATCH] x86/idt: Keep spurious entries unset in system_vectors
Vitaly Kuznetsov <vkuznets@...hat.com> writes:
> Commit dc20b2d52653 ("x86/idt: Move interrupt gate initialization to IDT
> code") had a side-effect of 'set_bit(i, used_vectors)' for unused entries
That was not a side effect. That was intentional.
> which are being mapped to spurious entries. (user_vectors were later
user_vectors?
> renamed to system_vectors).
>
> Previously, we used to count on system_vectors in arch_show_interrupts()
We used to? Maybe you used to. I did not.
> to not print unexisting entries in /proc/interrupts. E.g. 'Hypervisor
> callback interrupts' should not be printed on bare metal. This is
> currently broken.
That was definitely unintended, but that's a purely cosmetic issue.
> Setting bits in system_vectors for all unused entries also makes
> alloc_intr_gate() fail in case someone decides to do it later. It seems
> this is not currently an issue because all alloc_intr_gate() users are
> calling it early, before we call idt_setup_apic_and_irq_gates() but
> this also seems wrong.
No, that's not wrong. There is absolutely no reason to allocate an
interrupt gate later.
The only thing what's wrong is that alloc_intr_gate() lacks an __init
annotation and a sanity check to reject attempts which come in late
after idt_setup_apic_and_irq_gates() was invoked.
With that addressed we can remove the set_bit() for unused vectors to
cure the /proc/interrupts cosmetics.
Talking about side effects. This also reflects the actual number of
system vectors which are assigned in the debugfs interface as that was
'broken' as well.
Thanks,
tglx
8<--------------------
arch/x86/kernel/idt.c | 20 ++++++++++++++++----
drivers/xen/events/events_base.c | 24 +++++++++++++++---------
2 files changed, 31 insertions(+), 13 deletions(-)
--- a/arch/x86/kernel/idt.c
+++ b/arch/x86/kernel/idt.c
@@ -51,6 +51,9 @@ struct idt_data {
#define TSKG(_vector, _gdt) \
G(_vector, NULL, DEFAULT_STACK, GATE_TASK, DPL0, _gdt << 3)
+
+static __initdata bool idt_setup_done;
+
/*
* Early traps running on the DEFAULT_STACK because the other interrupt
* stacks work only after cpu_init().
@@ -318,11 +321,16 @@ void __init idt_setup_apic_and_irq_gates
#ifdef CONFIG_X86_LOCAL_APIC
for_each_clear_bit_from(i, system_vectors, NR_VECTORS) {
- set_bit(i, system_vectors);
+ /*
+ * Don't set the non assigned system vectors in the
+ * system_vectors bitmap. Otherwise they show up in
+ * /proc/interrupts.
+ */
entry = spurious_entries_start + 8 * (i - FIRST_SYSTEM_VECTOR);
set_intr_gate(i, entry);
}
#endif
+ idt_setup_done = true;
}
/**
@@ -352,6 +360,7 @@ void idt_invalidate(void *addr)
load_idt(&idt);
}
+/* This goes away once ASYNC_PF is sanitized */
void __init update_intr_gate(unsigned int n, const void *addr)
{
if (WARN_ON_ONCE(!test_bit(n, system_vectors)))
@@ -359,9 +368,12 @@ void __init update_intr_gate(unsigned in
set_intr_gate(n, addr);
}
-void alloc_intr_gate(unsigned int n, const void *addr)
+void __init alloc_intr_gate(unsigned int n, const void *addr)
{
- BUG_ON(n < FIRST_SYSTEM_VECTOR);
- if (!test_and_set_bit(n, system_vectors))
+ if (WARN_ON(n < FIRST_SYSTEM_VECTOR))
+ return;
+ if (WARN_ON(idt_setup_done))
+ return;
+ if (!WARN_ON(test_and_set_bit(n, system_vectors)))
set_intr_gate(n, addr);
}
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -1639,26 +1639,32 @@ EXPORT_SYMBOL_GPL(xen_set_callback_via);
/* Vector callbacks are better than PCI interrupts to receive event
* channel notifications because we can receive vector callbacks on any
* vcpu and we don't need PCI support or APIC interactions. */
-void xen_callback_vector(void)
+static void xen_callback_vector(void)
{
- int rc;
uint64_t callback_via;
if (xen_have_vector_callback) {
callback_via = HVM_CALLBACK_VECTOR(HYPERVISOR_CALLBACK_VECTOR);
- rc = xen_set_callback_via(callback_via);
- if (rc) {
+ if (xen_set_callback_via(callback_via)) {
pr_err("Request for Xen HVM callback vector failed\n");
xen_have_vector_callback = 0;
- return;
}
- pr_info_once("Xen HVM callback vector for event delivery is enabled\n");
- alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR,
- xen_hvm_callback_vector);
}
}
+
+static __init void xen_init_callback_vector(void)
+{
+ xen_callback_vector();
+ if (!xen_have_vector_callback)
+ return;
+
+ alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR, xen_hvm_callback_vector);
+ pr_info("Xen HVM callback vector for event delivery is enabled\n");
+}
+
#else
void xen_callback_vector(void) {}
+static inline void xen_init_callback_vector(void) {}
#endif
#undef MODULE_PARAM_PREFIX
@@ -1693,7 +1699,7 @@ void __init xen_init_IRQ(void)
pci_xen_initial_domain();
}
if (xen_feature(XENFEAT_hvm_callback_vector))
- xen_callback_vector();
+ xen_init_callback_vector();
if (xen_hvm_domain()) {
native_init_IRQ();
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