linux-kernel - Re: [PATCHv7 14/14] x86/tdx: Add unaccepted memory support

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Date:   Tue, 9 Aug 2022 14:45:44 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     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>,
        Mike Rapoport <rppt@...nel.org>,
        David Hildenbrand <david@...hat.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.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: [PATCHv7 14/14] x86/tdx: Add unaccepted memory support

On Tue, Jul 26, 2022 at 04:51:16PM +0200, Borislav Petkov wrote:
> On Tue, Jun 14, 2022 at 03:02:31PM +0300, Kirill A. Shutemov wrote:
> > +static bool is_tdx_guest(void)
> > +{
> > +	static bool once;
> > +	static bool is_tdx;
> > +
> > +	if (!IS_ENABLED(CONFIG_INTEL_TDX_GUEST))
> > +		return false;
> > +
> > +	if (!once) {
> > +		u32 eax, sig[3];
> > +
> > +		cpuid_count(TDX_CPUID_LEAF_ID, 0, &eax,
> > +			    &sig[0], &sig[2],  &sig[1]);
> > +		is_tdx = !memcmp(TDX_IDENT, sig, sizeof(sig));
> > +		once = true;
> > +	}
> > +
> > +	return is_tdx;
> > +}
> 
> early_tdx_detect() already calls this CPUID function. It assigns
> function pointers too.
> 
> So why can't you assign an accept_memory() function pointer there and
> get rid of this sprinkled if (tdx) everywhere?

This code called from EFI stub which runs before decompressor code and
therefore before early_tdx_detect().

> > diff --git a/arch/x86/boot/compressed/tdx.c b/arch/x86/boot/compressed/tdx.c
> > index 918a7606f53c..8518a75e5dd5 100644
> > --- a/arch/x86/boot/compressed/tdx.c
> > +++ b/arch/x86/boot/compressed/tdx.c
> > @@ -3,12 +3,15 @@
> >  #include "../cpuflags.h"
> >  #include "../string.h"
> >  #include "../io.h"
> > +#include "align.h"
> >  #include "error.h"
> > +#include "pgtable_types.h"
> >  
> >  #include <vdso/limits.h>
> >  #include <uapi/asm/vmx.h>
> >  
> >  #include <asm/shared/tdx.h>
> > +#include <asm/page_types.h>
> >  
> >  /* Called from __tdx_hypercall() for unrecoverable failure */
> >  void __tdx_hypercall_failed(void)
> > @@ -75,3 +78,78 @@ void early_tdx_detect(void)
> >  	pio_ops.f_outb = tdx_outb;
> >  	pio_ops.f_outw = tdx_outw;
> >  }
> > +
> > +static unsigned long try_accept_one(phys_addr_t start, unsigned long len,
> > +				    enum pg_level level)
> 
> That's pretty much a copy of the same function in arch/x86/coco/tdx/tdx.c.
> 
> Yeah, you need a tdx-shared.c which you include in both places just like
> it is done with sev-shared.c

Okay, will look into this.

> > +		accept_size = try_accept_one(start, len, PG_LEVEL_1G);
> > +		if (!accept_size)
> > +			accept_size = try_accept_one(start, len, PG_LEVEL_2M);
> > +		if (!accept_size)
> > +			accept_size = try_accept_one(start, len, PG_LEVEL_4K);
> > +		if (!accept_size)
> > +			error("Accepting memory failed\n");
> > +		start += accept_size;
> 
> This series of calls to try_accept_one() appear in at least three
> places. Please carve them out into a separate function can put it in
> tdx-shared.c.

Okay.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov