Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: x86: Spurious vectors not handled robustly
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        x86@kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
References: <e525108f-3749-4e1d-1ac2-0d0a2655f15f@siemens.com>
 <alpine.DEB.2.21.1906241204430.32342@nanos.tec.linutronix.de>
From:   Jan Kiszka <jan.kiszka@siemens.com>
Message-ID: <1565f016-4e3b-fa89-62e5-fc77594ee5aa@siemens.com>
Date:   Mon, 24 Jun 2019 12:21:27 +0200
User-Agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12)
 Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666
MIME-Version: 1.0
In-Reply-To: <alpine.DEB.2.21.1906241204430.32342@nanos.tec.linutronix.de>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 24.06.19 12:09, Thomas Gleixner wrote:
> Jan,
> 
> On Mon, 24 Jun 2019, Jan Kiszka wrote:
>> probably since "x86: Avoid building unused IRQ entry stubs" (2414e021ac8d),
>> the kernel can no longer tell spurious IRQs by the APIC apart from spuriously
>> triggered unused vectors.
> 
> Err. It does.
> 
>> We've managed to trigger such a cause with the Jailhouse hypervisor
>> (incorrectly injected MANAGED_IRQ_SHUTDOWN_VECTOR), and the result was
>> not only a misreport of the vector number (0xff instead of 0xef - took me
>> a while...), but also stalled interrupts of equal and lower priority
>> because a spurious interrupt is not (and must not be) acknowledged.
> 
> That does not make sense.
> 
> __visible void __irq_entry smp_spurious_interrupt(struct pt_regs *regs)
> {
>          u8 vector = ~regs->orig_ax;
>          u32 v;
> 
>          entering_irq();
>          trace_spurious_apic_entry(vector);
>          /*
>           * Check if this really is a spurious interrupt and ACK it
>           * if it is a vectored one.  Just in case...
>           */
>          v = apic_read(APIC_ISR + ((vector & ~0x1f) >> 1));
>          if (v & (1 << (vector & 0x1f)))
>                  ack_APIC_irq();
> 
> If it is a vectored one it _IS_ acked.
> 
>          inc_irq_stat(irq_spurious_count);
> 
>   	/* see sw-dev-man vol 3, chapter 7.4.13.5 */
>          pr_info("spurious APIC interrupt through vector %02x on CPU#%d, "
>                  "should never happen.\n", vector, smp_processor_id());
> 
> and the vector through which that comes is printed correctly, unless
> regs->orig_ax is hosed.

...which is exactly the case: Since that commit, all unused vectors share the 
same entry point, spurious_interrupt, see idt_setup_apic_and_irq_gates(). And 
that entry point sets orig_ax to ~0xff.

Jan

-- 
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux