linux-kernel - Re: [PATCHv3 2/3] x86/tdx: Clarify RIP adjustments in #VE handler

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Date:   Thu, 26 May 2022 13:18:23 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        luto@...nel.org, peterz@...radead.org, ak@...ux.intel.com,
        dan.j.williams@...el.com, david@...hat.com, hpa@...or.com,
        linux-kernel@...r.kernel.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com, seanjc@...gle.com,
        thomas.lendacky@....com, x86@...nel.org
Subject: Re: [PATCHv3 2/3] x86/tdx: Clarify RIP adjustments in #VE handler

On 5/26/22 13:13, Kirill A. Shutemov wrote:
>> I'm not super happy with how this comment ended up.  First, let's put
>> the comment next to the code to which it applies, like:
>>
>> 	/*
>> 	 * ve->instr_len is not defined for EPT violations.  For those,
>> 	 * the kernel must decode instructions manually and should not
>> 	 * be using this function.
>> 	 */
>> 	if (WARN_ON_ONCE(ve->exit_reason == EXIT_REASON_EPT_VIOLATION))
>> 		return 0;
>>
>> 	/*
>> 	 * Assume that the #VE occurred due to instruction execution.
>> 	 */
>> 	return ve->instr_len;
> Would it be helpful if the function has a whitelist of exit resons where
> using ve->instr_len is safe? WARN_ONCE() and return 0 otherwise.

Maybe.  I was hoping to avoid mostly duplicating the
virt_exception_kernel() switch().