linux-kernel - Re: [RFC PATCH V2 15/18] x86/sev: Add a #HV exception handler

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Date:   Tue, 10 Jan 2023 21:43:56 +0800
From:   Tianyu Lan <ltykernel@...il.com>
To:     "Gupta, Pankaj" <pankaj.gupta@....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 V2 15/18] x86/sev: Add a #HV exception handler

On 1/10/2023 8:47 PM, Gupta, Pankaj wrote:
>> + *
>> + * To make this work the #HV entry code tries its best to pretend it 
>> doesn't use
>> + * an IST stack by switching to the task stack if coming from 
>> user-space (which
>> + * includes early SYSCALL entry path) or back to the stack in the 
>> IRET frame if
>> + * entered from kernel-mode.
>> + *
>> + * If entered from kernel-mode the return stack is validated first, 
>> and if it is
>> + * not safe to use (e.g. because it points to the entry stack) the 
>> #HV handler
>> + * will switch to a fall-back stack (HV2) and call a special handler 
>> function.
>> + *
>> + * The macro is only used for one vector, but it is planned to be 
>> extended in
>> + * the future for the #HV exception.
> 
> Noticed same comment line in the #VC exception handling section (macro 
> idtentry_vc). Just wondering we need to remove this line as the patch 
> being proposed for the #HV exception handling? unless this is planned to 
> be extended in some other way.

Nice catch! Will remove this in the next version.

Thanks.