linux-kernel - Re: [PATCH v3 01/18] KVM: arm64: Change the layout of enum pkvm_page

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Message-ID: <Z2F3rveiCEuPwxhN@google.com>
Date: Tue, 17 Dec 2024 13:07:58 +0000
From: Quentin Perret <qperret@...gle.com>
To: Marc Zyngier <maz@...nel.org>
Cc: Oliver Upton <oliver.upton@...ux.dev>, Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Fuad Tabba <tabba@...gle.com>,
	Vincent Donnefort <vdonnefort@...gle.com>,
	Sebastian Ene <sebastianene@...gle.com>,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 01/18] KVM: arm64: Change the layout of enum
 pkvm_page_state

On Tuesday 17 Dec 2024 at 10:52:08 (+0000), Marc Zyngier wrote:
> On Mon, 16 Dec 2024 17:57:46 +0000,
> Quentin Perret <qperret@...gle.com> wrote:
> > 
> > The 'concrete' (a.k.a non-meta) page states are currently encoded using
> > software bits in PTEs. For performance reasons, the abstract
> > pkvm_page_state enum uses the same bits to encode these states as that
> > makes conversions from and to PTEs easy.
> > 
> > In order to prepare the ground for moving the 'concrete' state storage
> > to the hyp vmemmap, re-arrange the enum to use bits 0 and 1 for this
> > purpose.
> > 
> > No functional changes intended.
> > 
> > Signed-off-by: Quentin Perret <qperret@...gle.com>
> > ---
> >  arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 16 +++++++++-------
> >  1 file changed, 9 insertions(+), 7 deletions(-)
> > 
> > diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> > index 0972faccc2af..8c30362af2b9 100644
> > --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> > +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h
> > @@ -24,25 +24,27 @@
> >   */
> >  enum pkvm_page_state {
> >  	PKVM_PAGE_OWNED			= 0ULL,
> > -	PKVM_PAGE_SHARED_OWNED		= KVM_PGTABLE_PROT_SW0,
> > -	PKVM_PAGE_SHARED_BORROWED	= KVM_PGTABLE_PROT_SW1,
> > -	__PKVM_PAGE_RESERVED		= KVM_PGTABLE_PROT_SW0 |
> > -					  KVM_PGTABLE_PROT_SW1,
> > +	PKVM_PAGE_SHARED_OWNED		= BIT(0),
> > +	PKVM_PAGE_SHARED_BORROWED	= BIT(1),
> > +	__PKVM_PAGE_RESERVED		= BIT(0) | BIT(1),
> >  
> >  	/* Meta-states which aren't encoded directly in the PTE's SW bits */
> > -	PKVM_NOPAGE,
> > +	PKVM_NOPAGE			= BIT(2),
> >  };
> > +#define PKVM_PAGE_META_STATES_MASK	(~(BIT(0) | BIT(1)))
> 
> Shouldn't that be ~__PKVM_PAGE_RESERVED, given that you just defined it?

Sure thing, I followed the same pattern as PKVM_PAGE_STATE_PROT_MASK
which was explicit in which bits it sets, but very happy to change.

> >  
> >  #define PKVM_PAGE_STATE_PROT_MASK	(KVM_PGTABLE_PROT_SW0 | KVM_PGTABLE_PROT_SW1)
> >  static inline enum kvm_pgtable_prot pkvm_mkstate(enum kvm_pgtable_prot prot,
> >  						 enum pkvm_page_state state)
> >  {
> > -	return (prot & ~PKVM_PAGE_STATE_PROT_MASK) | state;
> > +	prot &= ~PKVM_PAGE_STATE_PROT_MASK;
> > +	prot |= FIELD_PREP(PKVM_PAGE_STATE_PROT_MASK, state);
> > +	return prot;
> >  }
> >  
> >  static inline enum pkvm_page_state pkvm_getstate(enum kvm_pgtable_prot prot)
> >  {
> > -	return prot & PKVM_PAGE_STATE_PROT_MASK;
> > +	return FIELD_GET(PKVM_PAGE_STATE_PROT_MASK, prot);
> >  }
> >  
> >  struct host_mmu {
> 
> Thanks,
> 
> 	M.
> 
> -- 
> Without deviation from the norm, progress is not possible.