linux-kernel - Re: [RFC PATCH V2 16/18] x86/sev: Initialize #HV doorbell and handle interrupt requests

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Date:   Tue, 22 Nov 2022 21:46:14 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     "Kalra, Ashish" <ashish.kalra@....com>, luto@...nel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        seanjc@...gle.com, pbonzini@...hat.com, jgross@...e.com,
        tiala@...rosoft.com, kirill@...temov.name,
        jiangshan.ljs@...group.com, peterz@...radead.org,
        srutherford@...gle.com, akpm@...ux-foundation.org,
        anshuman.khandual@....com, pawan.kumar.gupta@...ux.intel.com,
        adrian.hunter@...el.com, daniel.sneddon@...ux.intel.com,
        alexander.shishkin@...ux.intel.com, sandipan.das@....com,
        ray.huang@....com, brijesh.singh@....com, michael.roth@....com,
        thomas.lendacky@....com, venu.busireddy@...cle.com,
        sterritt@...gle.com, tony.luck@...el.com, samitolvanen@...gle.com,
        fenghua.yu@...el.com
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-arch@...r.kernel.org
Subject: Re: [RFC PATCH V2 16/18] x86/sev: Initialize #HV doorbell and handle
 interrupt requests

On 11/21/2022 11:05 PM, Kalra, Ashish wrote:
>> +static void do_exc_hv(struct pt_regs *regs)
>> +{
>> +    union hv_pending_events pending_events;
>> +    u8 vector;
>> +
>> +    while (sev_hv_pending()) {
>> +        asm volatile("cli" : : : "memory");
>> +
> 
> Do we really need to disable interrupts here, #HV exception will be 
> dispatched via an interrupt gate in the IDT, so interrupts should be 
> implicitly disabled, right ?
>>    panic("Unexpected vector %d\n", vector);
>> +                unreachable();
>> +            }
>> +        } else {
>> +            common_interrupt(regs, pending_events.vector);
>> +        }
>> +
>> +        asm volatile("sti" : : : "memory");
> 
> Again, why do we need to re-enable interrupts here (in this loop), 
> interrupts will get re-enabled in the irqentry_exit() code path ?

Hi Ashish:
	Thanks for your review.	check_hv_pending() is also called in the
native_irq_enable() to handle some pending interrupt requests after re
-enabling interrupt. For such case, disables irq when handle exception
or interrupt event.