Re: [PATCH 04/16] KVM: arm64: Add MMIO checking infrastructure

[Marc Zyngier]

On Tue, 20 Jul 2021 16:49:45 +0100,
Quentin Perret <qperret@xxxxxxxxxx> wrote:
> 
> On Tuesday 20 Jul 2021 at 14:15:56 (+0100), Marc Zyngier wrote:
> > On Tue, 20 Jul 2021 12:13:20 +0100,
> > Quentin Perret <qperret@xxxxxxxxxx> wrote:
> > > 
> > > On Thursday 15 Jul 2021 at 17:31:47 (+0100), Marc Zyngier wrote:
> > > > +struct s2_walk_data {
> > > > +	kvm_pte_t	pteval;
> > > > +	u32		level;
> > > > +};
> > > > +
> > > > +static int s2_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
> > > > +		     enum kvm_pgtable_walk_flags flag, void * const arg)
> > > > +{
> > > > +	struct s2_walk_data *data = arg;
> > > > +
> > > > +	data->level = level;
> > > > +	data->pteval = *ptep;
> > > > +	return 0;
> > > > +}
> > > > +
> > > > +/* Assumes mmu_lock taken */
> > > > +static bool __check_ioguard_page(struct kvm_vcpu *vcpu, gpa_t ipa)
> > > > +{
> > > > +	struct s2_walk_data data;
> > > > +	struct kvm_pgtable_walker walker = {
> > > > +		.cb             = s2_walker,
> > > > +		.flags          = KVM_PGTABLE_WALK_LEAF,
> > > > +		.arg            = &data,
> > > > +	};
> > > > +
> > > > +	kvm_pgtable_walk(vcpu->arch.hw_mmu->pgt, ALIGN_DOWN(ipa, PAGE_SIZE),
> > > > +			 PAGE_SIZE, &walker);
> > > > +
> > > > +	/* Must be a PAGE_SIZE mapping with our annotation */
> > > > +	return (BIT(ARM64_HW_PGTABLE_LEVEL_SHIFT(data.level)) == PAGE_SIZE &&
> > > > +		data.pteval == MMIO_NOTE);
> > > 
> > > Nit: you could do this check in the walker directly and check the return
> > > value of kvm_pgtable_walk() instead. That would allow to get rid of
> > > struct s2_walk_data.
> > > 
> > > Also, though the compiler might be able to optimize, maybe simplify the
> > > level check to level == (KVM_PGTABLE_MAX_LEVELS - 1)?
> > 
> > Yup, all good points. I guess I could do the same in my other series
> > that parses the userspace PT to extract the level.
> 
> Well, actually, let me take that back. I think something like you have
> would be useful, but in pgtable.c directly and re-usable for stage-1 and
> stage-2 walks. Maybe something like the below (totally untested)?
> 
> I could use such a walker in several places as well in the memory
> ownership series:
> 
>  - following the idea of [1], I could remove the
>    kvm_pgtable_stage2_find_range() function entirely;
> 
>  - [2] defines 2 custom walkers that do nothing but walk host stage-2
>    and hyp stage-1 page-tables to check permissions and such --  they
>    could be removed/re-implemented easily as well.
> 
> And you seem to need something similar here, so clearly there is a need.
> WDYT?

So FWIW, I've now pushed out an updated series for the THP changes[1],
and you will find a similar patch at the base of the branch. Please
have a look and let me know what you think!

Thanks,

	M.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=kvm-arm64/mmu/mapping-levels

-- 
Without deviation from the norm, progress is not possible.