linux-kernel - Re: [PATCH v8 5/6] KVM: arm64: Initialize the ptdump parser with stage-2 attributes

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Message-ID: <Zsgcdjh4EvqFWMlA@google.com>
Date: Fri, 23 Aug 2024 05:21:58 +0000
From: Sebastian Ene <sebastianene@...gle.com>
To: Marc Zyngier <maz@...nel.org>
Cc: akpm@...ux-foundation.org, alexghiti@...osinc.com, ankita@...dia.com,
	ardb@...nel.org, catalin.marinas@....com,
	christophe.leroy@...roup.eu, james.morse@....com,
	vdonnefort@...gle.com, mark.rutland@....com, oliver.upton@...ux.dev,
	rananta@...gle.com, ryan.roberts@....com, shahuang@...hat.com,
	suzuki.poulose@....com, will@...nel.org, yuzenghui@...wei.com,
	kvmarm@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v8 5/6] KVM: arm64: Initialize the ptdump parser with
 stage-2 attributes

On Thu, Aug 22, 2024 at 05:15:54PM +0100, 'Marc Zyngier' via kernel-team wrote:
> On Tue, 20 Aug 2024 15:20:25 +0100,
> Marc Zyngier <maz@...nel.org> wrote:
> > 
> > On Fri, 16 Aug 2024 13:39:05 +0100,
> > Sebastian Ene <sebastianene@...gle.com> wrote:
> > > 
> > > Define a set of attributes used by the ptdump parser to display the
> > > properties of a guest memory region covered by a pagetable descriptor.
> > > Build a description of the pagetable levels and initialize the parser
> > > with this configuration.
> > > 
> > > Signed-off-by: Sebastian Ene <sebastianene@...gle.com>
> > > ---
> > >  arch/arm64/kvm/ptdump.c | 135 ++++++++++++++++++++++++++++++++++++++--
> > >  1 file changed, 129 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
> > > index 52483d56be2e..79be07ec3c3c 100644
> > > --- a/arch/arm64/kvm/ptdump.c
> > > +++ b/arch/arm64/kvm/ptdump.c
> > > @@ -14,6 +14,51 @@
> > >  #include <kvm_ptdump.h>
> > >  
> > >  
> > > +#define MARKERS_LEN		(2)
> > > +#define KVM_PGTABLE_MAX_LEVELS	(KVM_PGTABLE_LAST_LEVEL + 1)
> > > +
> > > +struct kvm_ptdump_guest_state {
> > > +	struct kvm		*kvm;
> > > +	struct ptdump_pg_state	parser_state;
> > > +	struct addr_marker	ipa_marker[MARKERS_LEN];
> > > +	struct ptdump_pg_level	level[KVM_PGTABLE_MAX_LEVELS];
> > > +	struct ptdump_range	range[MARKERS_LEN];
> > > +};
> > > +
> > > +static const struct ptdump_prot_bits stage2_pte_bits[] = {
> > > +	{
> > > +		.mask	= PTE_VALID,
> > > +		.val	= PTE_VALID,
> > > +		.set	= " ",
> > > +		.clear	= "F",
> > > +	}, {
> > > +		.mask	= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R | PTE_VALID,
> > > +		.val	= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_R | PTE_VALID,
> > > +		.set	= "R",
> > > +		.clear	= " ",
> > > +	}, {
> > > +		.mask	= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W | PTE_VALID,
> > > +		.val	= KVM_PTE_LEAF_ATTR_LO_S2_S2AP_W | PTE_VALID,
> > > +		.set	= "W",
> > > +		.clear	= " ",
> > > +	}, {
> > > +		.mask	= KVM_PTE_LEAF_ATTR_HI_S2_XN | PTE_VALID,
> > > +		.val	= PTE_VALID,
> > > +		.set	= " ",
> > > +		.clear	= "X",
> > > +	}, {
> > > +		.mask	= KVM_PTE_LEAF_ATTR_LO_S2_AF | PTE_VALID,
> > > +		.val	= KVM_PTE_LEAF_ATTR_LO_S2_AF | PTE_VALID,
> > > +		.set	= "AF",
> > > +		.clear	= "  ",
> > > +	}, {
> > > +		.mask	= PTE_TABLE_BIT | PTE_VALID,
> > > +		.val	= PTE_VALID,
> > > +		.set	= "BLK",
> > > +		.clear	= "   ",
> > > +	},
> > > +};
> > > +
> > >  static int kvm_ptdump_visitor(const struct kvm_pgtable_visit_ctx *ctx,
> > >  			      enum kvm_pgtable_walk_flags visit)
> > >  {
> > > @@ -40,15 +85,81 @@ static int kvm_ptdump_show_common(struct seq_file *m,
> > >  	return kvm_pgtable_walk(pgtable, 0, BIT(pgtable->ia_bits), &walker);
> > >  }
> > >  
> > > +static int kvm_ptdump_build_levels(struct ptdump_pg_level *level, u32 start_lvl)
> > > +{
> > > +	static const char * const level_names[] = {"PGD", "PUD", "PMD", "PTE"};
> > 
> > How about 5 level page tables, which we support since v6.8? The
> > architecture uses a SL=-1 in this case, and I have the feeling this is
> > going to expose in a lovely way, given that you use a u32 for
> > start_level... :-/
> 

Hello Marc,

> Talking to Oliver, I just had an epiphany: we never have a 5th level
> with KVM, because we always use concatenated page tables at the start
> level. So the depth is still 4 levels, but we get up to 16 pages at
> level 0, and that's how we expand the IPA space from 48 to 52 bits.
> 

Thanks for letting me know. Then it should be fine keeping that as an
unisgned integer.

> So by the look of it, your code should still be OK with only 4 levels.
> 

Thanks,
Seb

> Apologies for leading you in the wrong direction.
> 
> 	M.
> 
> -- 
> Without deviation from the norm, progress is not possible.
> 
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