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Date: Tue, 28 Apr 2020 08:43:23 +0200
From: Vitaly Kuznetsov <vkuznets@...hat.com>
To: Thomas Gleixner <tglx@...utronix.de>
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
Thomas Gleixner <tglx@...utronix.de> writes:
> 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?
*used*
>
>> 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.
I was referring to
commit 9d87cd61a6b71ee00b7576a3ebc10208becdbea1
Author: Vitaly Kuznetsov <vkuznets@...hat.com>
Date: Tue Jul 7 18:26:13 2015 +0200
x86/irq: Hide 'HYP:' line in /proc/interrupts when not on Xen/Hyper-V
and right you are, it lacks your Signed-off-by :-)
>
>> 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.
Ok, I was only aiming at fixing the cosmetics but making
alloc_intr_gate() __init seems to make sense too.
>
> 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 */
Rumor has it that the work is ongoing...
> 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();
I don't quite like the 'xen_callback_vector()' name, it sounds like it
is the irq handler but it's not. If we are to split the
alloc_intr_gate() part I'd suggest the following:
xen_alloc_callback_vector() -> alloc_intr_gate()
xen_setup_callback_vector() -> hypercall
Juergen, what do you think?
> + 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();
>
Ok, I'll split this into several patches, write 'to-be-massaged'
changelogs and send v2 out. Thanks!
--
Vitaly
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