linux-kernel - Re: [PATCHv5 10/12] x86/tdx: Unaccepted memory support

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Message-ID: <20220511011906.el4m54fns7ilh7fr@box.shutemov.name>
Date:   Wed, 11 May 2022 04:19:06 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <jroedel@...e.de>,
        Ard Biesheuvel <ardb@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Tom Lendacky <thomas.lendacky@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Varad Gautam <varad.gautam@...e.com>,
        Dario Faggioli <dfaggioli@...e.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>, x86@...nel.org,
        linux-mm@...ck.org, linux-coco@...ts.linux.dev,
        linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv5 10/12] x86/tdx: Unaccepted memory support

On Fri, May 06, 2022 at 11:44:23PM +0300, Kirill A. Shutemov wrote:
> > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > > index 7021ec725dd3..e4c31dbea6d7 100644
> > > --- a/arch/x86/Kconfig
> > > +++ b/arch/x86/Kconfig
> > > @@ -885,6 +885,7 @@ config INTEL_TDX_GUEST
> > >  	select ARCH_HAS_CC_PLATFORM
> > >  	select X86_MEM_ENCRYPT
> > >  	select X86_MCE
> > > +	select UNACCEPTED_MEMORY
> > 
> > WARNING: unmet direct dependencies detected for UNACCEPTED_MEMORY
> >   Depends on [n]: EFI [=y] && EFI_STUB [=y] && !KEXEC_CORE [=y]
> >   Selected by [y]:
> >   - INTEL_TDX_GUEST [=y] && HYPERVISOR_GUEST [=y] && X86_64 [=y] && CPU_SUP_INTEL [=y] && X86_X2APIC [=y]
> > 
> > WARNING: unmet direct dependencies detected for UNACCEPTED_MEMORY
> >   Depends on [n]: EFI [=y] && EFI_STUB [=y] && !KEXEC_CORE [=y]
> >   Selected by [y]:
> >   - INTEL_TDX_GUEST [=y] && HYPERVISOR_GUEST [=y] && X86_64 [=y] && CPU_SUP_INTEL [=y] && X86_X2APIC [=y]
> 
> Ughh. Any ideas how to get around it? (Except for implementing kexec
> support right away?)

I reworked this to boot-time kexec disable.


> > Also, it doesn't need to be bool - you can simply return accept_size on
> > success and 0 on error so that you don't have an I/O argument.
> 
> So on the calling side it would look like:
> 
> 	accepted = try_accept_one(start, len, PG_LEVEL_1G)
> 	if (accepted) {
> 		start += accepted;
> 		continue;
> 	}
> 
> And the similar for other levels. Is it really better?

JFYI, I've reworked it as

		accepted = try_accept_one(start, len, PG_LEVEL_1G);
		if (!accepted)
			accepted = try_accept_one(start, len, PG_LEVEL_2M);
		if (!accepted)
			accepted = try_accept_one(start, len, PG_LEVEL_4K);
		if (!accepted)
			return false;
		start += accepted;

looks good to me.

-- 
 Kirill A. Shutemov