linux-kernel - Re: [RFC PATCH 16/17] x86/sev: Add a #HV exception handler

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Date:   Mon, 14 Nov 2022 09:28:31 +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 16/17] x86/sev: Add a #HV exception handler

Thanks for your review.

On 11/11/2022 4:38 AM, Kalra, Ashish wrote:
>> +    UNWIND_HINT_REGS
>> +
>> +    /* Update pt_regs */
>> +    movq    ORIG_RAX(%rsp), %rsi    /* get error code into 2nd 
>> argument*/
>> +    movq    $-1, ORIG_RAX(%rsp)    /* no syscall to restart */
>> +
>> +    movq    %rsp, %rdi        /* pt_regs pointer */
>> +    call    kernel_\cfunc
>> +
>> +    jmp    paranoid_exit
>> +
>> +.Lfrom_usermode_switch_stack_\@:
>> +    idtentry_body user_\cfunc, has_error_code=1
> 
> #HV exception handler cannot/does not inject an error code, so shouldn't
> has_error_code == 0?

Nice catch. Will update in the next version.

>> +    irqentry_state_t irq_state;
>> +
>> +    if (unlikely(on_hv_fallback_stack(regs))) {
>> +            instrumentation_begin();
>> +            panic("Can't handle #HV exception from unsupported 
>> context\n");
>> +            instrumentation_end();
>> +    }
> 
> HV fallback stack exists and is used if we couldn't switch to HV stack. 
> If we have to issue a panic() here, why don't we simply issue the 
> panic() in hv_switch_off_ist(), when we couldn't switch to HV stack ?
> 

Yes, this is a good idea. Will update. Thanks.