linux-kernel - Re: [RFC PATCH V3 00/16] x86/hyperv/sev: Add AMD sev-snp enlightened guest support on hyperv

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Date:   Fri, 10 Mar 2023 16:35:38 +0100
From:   "Gupta, Pankaj" <pankaj.gupta@....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,
        ashish.kalra@....com, 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 V3 00/16] x86/hyperv/sev: Add AMD sev-snp enlightened
 guest support on hyperv



Hi Tianyu,

While testing the guest patches on KVM host, My guest kernel is stuck
at early bootup. As it did not seem a hang but sort of loop where 
interrupts are getting processed from "pv_native_irq_enable" path 
repeatedly and prevent boot process to make progress IIUC. Did you face 
any such scenario in your testing?

It seems to me "native_irq_enable" enable interrupts and 
"check_hv_pending_irq_enable" starts handling the interrupts (after 
disabling irqs). But "check_hv_pending_irq_enable=>do_exc_hv" can again 
call "pv_native_irq_enable" in interrupt handling path and execute the 
same loop?

Also pasting below the stack dump [1].

Thanks,
Pankaj

[1]
[   20.530786] Call Trace:^M
[   20.531099]  <IRQ>^M
[   20.531360]  dump_stack_lvl+0x4d/0x67^M
[   20.531820]  dump_stack+0x14/0x1a^M
[   20.532235]  do_exc_hv.cold+0x11/0xec^M
[   20.532792]  check_hv_pending_irq_enable+0x64/0x80^M
[   20.533390]  pv_native_irq_enable+0xe/0x20^M   ====> here
[   20.533902]  __do_softirq+0x89/0x2f3^M
[   20.534352]  __irq_exit_rcu+0x9f/0x110^M
[   20.534825]  irq_exit_rcu+0x12/0x20^M
[   20.535267]  common_interrupt+0xca/0xf0^M
[   20.535745]  </IRQ>^M
[   20.536014]  <TASK>^M
[   20.536286]  do_exc_hv.cold+0xda/0xec^M
[   20.536826]  check_hv_pending_irq_enable+0x64/0x80^M
[   20.537429]  pv_native_irq_enable+0xe/0x20^M    ====> here
[   20.537942]  _raw_spin_unlock_irqrestore+0x21/0x50^M
[   20.538539]  __setup_irq+0x3be/0x740^M
[   20.538990]  request_threaded_irq+0x116/0x180^M
[   20.539533]  hpet_time_init+0x35/0x56^M
[   20.539994]  x86_late_time_init+0x1f/0x3d^M
[   20.540556]  start_kernel+0x8af/0x970^M
[   20.541033]  x86_64_start_reservations+0x28/0x2e^M
[   20.541607]  x86_64_start_kernel+0x96/0xa0^M
[   20.542126]  secondary_startup_64_no_verify+0xe5/0xeb^M
[   20.542757]  </TASK>^M