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:   Wed, 15 Mar 2023 07:40:16 +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,

>> 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?
> 
> 
> I don't meet the issue. Thanks for report. I will double check and 
> report back.

Thank you!

More testing with the patches: After I commented out "do_exc_hv" from
pv_native_irq_enable()->check_hv_pending_irq_enable() code path. Now, I 
am getting below [2] stack trace repeatedly when I dump stack.

This seems to me after IST stack return from #VC handling
for "native_cpuid", paranoid_exit =>"do_exc_hv" is handling interrupts. 
As we don't disable interrupts in check_hv_pending()=>do_exc_hv(), so 
interrupts are handled continuously here. This also prevents the boot 
processor to make progress and stuck here.

Thoughts please? as I might be missing some important details here.

Thanks,
Pankaj

[2]

[   59.845396] Call Trace:^M
[   59.845703]  <TASK>^M
[   59.845980]  dump_stack_lvl+0x4d/0x67^M
[   59.846432]  dump_stack+0x14/0x1a^M
[   59.846842]  do_exc_hv.cold+0x22/0xfd^M
[   59.847301]  check_hv_pending+0x38/0x50^M
[   59.847773]  paranoid_exit+0x8/0x70^M
[   59.848205] RIP: 0010:native_cpuid+0x19/0x30^M
[   59.848729] Code: 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 
f3 0f 1e fa 55 49 89 f8 49 89 c9 48 89 d7 41 8b 00 48 89 e5 53 8b 0a 0f 
a2 <41> 89 00 89 1e 48 8b 5d f8 89 0f 41 89 11 c9 e9 f7 bc df 00 0f 1f^M
[   59.850995] RSP: 0000:ffffffffbd403e48 EFLAGS: 00010202^M
[   59.851636] RAX: 000000000100007b RBX: 0000000000000000 RCX: 
0000000000000000^M
[   59.852498] RDX: 0000000000000000 RSI: ffffffffbd403e64 RDI: 
ffffffffbd403e68^M
[   59.853361] RBP: ffffffffbd403e50 R08: ffffffffbd403e60 R09: 
ffffffffbd403e6c^M
[   59.854240] R10: ffffffffbd403d10 R11: ffff9af5bff3cfe8 R12: 
0000000000000056^M
[   59.855111] R13: ffff9af5bffc8e40 R14: 0000000000000000 R15: 
ffffffffbd41a120^M
[   59.855976]  kvm_arch_para_features+0x4e/0x80^M
[   59.856511]  pv_ipi_supported+0xe/0x34^M
[   59.856973]  kvm_apic_init+0x12/0x3f^M
[   59.857414]  apic_intr_mode_init+0x8d/0x10d^M
[   59.857939]  x86_late_time_init+0x28/0x3d^M
[   59.858435]  start_kernel+0x8af/0x970^M
[   59.858894]  x86_64_start_reservations+0x28/0x2e^M
[   59.859461]  x86_64_start_kernel+0x96/0xa0^M
[   59.859965]  secondary_startup_64_no_verify+0xe5/0xeb^M
[   59.860583]  </TASK>^M