Re: [PATCH 02/20] KVM: arm64: Add support for creating kernel-agnostic stage-1 page tables

[Quentin Perret <qperret@google.com>]

On Friday 31 Jul 2020 at 09:14:36 (+0100), Quentin Perret wrote:
> Hey Will,
> 
> On Thursday 30 Jul 2020 at 16:33:48 (+0100), Will Deacon wrote:
> > +void *kvm_pgtable_hyp_alloc_cookie(u32 va_bits)
> > +{
> > +	struct kvm_pgtable *pgt = kzalloc(sizeof(*pgt), GFP_KERNEL);
> > +
> > +	if (!pgt)
> > +		return NULL;
> > +
> > +	pgt->ia_bits = va_bits;
> > +	pgt->start_level = kvm_start_level(va_bits);
> > +
> > +	pgt->pgd = (kvm_pte_t *)get_zeroed_page(GFP_KERNEL);
> > +	if (!pgt->pgd) {
> > +		kfree(pgt);
> > +		pgt = NULL;
> > +	}
> > +
> > +	return pgt;
> > +}
> > +
> > +static int hyp_free_walker(u64 addr, u64 end, u32 level, kvm_pte_t *ptep,
> > +			   enum kvm_pgtable_walk_flags flag, void * const arg)
> > +{
> > +	free_page((unsigned long)kvm_pte_follow(*ptep));
> > +	return 0;
> > +}
> > +
> > +void kvm_pgtable_hyp_free_cookie(void *cookie)
> > +{
> > +	size_t pgd_sz;
> > +	struct kvm_pgtable *pgt = cookie;
> > +	struct kvm_pgtable_walker walker = {
> > +		.cb	= hyp_free_walker,
> > +		.flags	= KVM_PGTABLE_WALK_TABLE_POST,
> > +	};
> > +
> > +	if (kvm_pgtable_walk(cookie, 0, BIT(pgt->ia_bits), &walker))
> > +		kvm_err("Failed to free page-table pages\n");
> > +
> > +	pgd_sz = kvm_pgd_pages(pgt) * PAGE_SIZE;
> > +	free_pages_exact(pgt->pgd, pgd_sz);
> 
> Given that the pgd is unconditionally a single page for the stage 1 case
> (as per kvm_pgtable_hyp_alloc_cookie() above), should we simplify this
> to a simple free_page()? Or did you want to factorize this with the
> stage 2 free path?

Hmm, or maybe it's the alloc() path that needs fixing actually ...
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