linux-kernel - Re: [PATCH v3 10/16] KVM: selftests: Reuse virt mapping functions for nested EPTs

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Message-ID: <6udca7kfrwy6gzads46r2eczyaapiav6h37y5e4oqxsdpl6j7h@oj5x5qr6d5jw>
Date: Tue, 23 Dec 2025 23:47:37 +0000
From: Yosry Ahmed <yosry.ahmed@...ux.dev>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 10/16] KVM: selftests: Reuse virt mapping functions
 for nested EPTs

On Tue, Dec 23, 2025 at 03:14:28PM -0800, Sean Christopherson wrote:
> On Thu, Nov 27, 2025, Yosry Ahmed wrote:
> > +	/*
> > +	 * EPTs do not have 'present' or 'user' bits, instead bit 0 is the
> > +	 * 'readable' bit. In some cases, EPTs can be execute-only and an entry
> > +	 * is present but not readable. However, for the purposes of testing we
> > +	 * assume 'present' == 'user' == 'readable' for simplicity.
> > +	 */
> > +	pte_masks = (struct pte_masks){
> > +		.present	=	BIT_ULL(0),
> > +		.user		=	BIT_ULL(0),
> > +		.writable	=	BIT_ULL(1),
> > +		.x		=	BIT_ULL(2),
> > +		.accessed	=	BIT_ULL(5),
> > +		.dirty		=	BIT_ULL(6),
> 
> Almost forgot, the Accessed and Dirty bits are wrong.  They are bits 8 and 9
> respectively, not 5 and 6.  Amusingly (well, it's amusing *now*, it wasn't so
> amusing at the time), I found that out when I couldn't get KVM to create a writable
> SPTE on a read fault in the nested dirty log test :-)

Instead of being a reasonable person and own up to my mistake, I will
blame Intel for putting the bits there to begin with :P

(But seriously, sorry for such a dumb mistake)