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 13:17:31 -0600
From:   "Kalra, Ashish" <ashish.kalra@....com>
To:     Tianyu Lan <ltykernel@...il.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 11/22/2022 7:46 AM, Tianyu Lan wrote:
> 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.
> 

Then probably add the interrupt disable/enable in the caller
function like native_irq_enable() which seems logical as 
check_hv_pending() is always called with interrupts disabled (either via 
HW or SW) and also interrupt disable/enable seems redundant in 
check_hv_pending().

Thanks,
Ashish