linux-kernel - Re: [PATCH v8 06/11] x86/traps: Add #VE support for TDX guest

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Date:   Thu, 7 Oct 2021 10:22:16 -0700
From:   "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>, Deep Shah <sdeep@...are.com>,
        VMware Inc <pv-drivers@...are.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Peter H Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 06/11] x86/traps: Add #VE support for TDX guest



On 10/7/21 10:06 AM, Borislav Petkov wrote:
> Same question as before - why do you need to clear this @out thing above
> when __tdx_module_call() will overwrite it?

Now checking again, I think we don't to initialize the @out pointer. I will
fix this in call cases.

But for tdx_get_ve_info() case, we are updating the @ve pointer without
checking the tdcall return value and __tdx_module_call() will update the
@out only if tdcall is successful. Currently due to @out=0 initialization,
this logic does not cause any issue. But to properly fix it, I need to
check for tdcall return value before updating the @ve value.

> 
> What you should do instead is check that @ve pointer which you get
> passed in - it might be NULL.

Current use case of tdx_get_ve_info() can never be NULL. But if you
want to add this check for possible future issues, I can do it.

arch/x86/kernel/traps.c:1205:	ret = tdx_get_ve_info(&ve);
arch/x86/kernel/tdx.c:945:	if (tdx_get_ve_info(&ve))


-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer