Re: [PATCH v3 2/3] KVM: arm64: Introduce KVM_PGTABLE_WALK_SKIP_LEVEL* walk flags

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] KVM_PGTABLE_WALK_SKIP_LEVEL* flags fail to skip the starting root level of the page table walk.
--

--- Patch [2]: [PATCH v3 2/3] KVM: arm64: Introduce KVM_PGTABLE_WALK_SKIP_LEVEL* walk flags ---
commit 5ddf63ba492be8c2a84af0b81cf00790fc72767a
Author: Leonardo Bras <leo.bras@arm.com>

KVM: arm64: Introduce KVM_PGTABLE_WALK_SKIP_LEVEL* walk flags

This commit adds new walking flags that tell kvm_pgtable_walk() to skip
lower levels when traversing page tables.

> diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
> index 4be1d51a6ac58..b9a2078efc519 100644
> --- a/arch/arm64/kvm/hyp/pgtable.c
> +++ b/arch/arm64/kvm/hyp/pgtable.c

[ ... ]

> @@ -192,7 +205,7 @@ static inline int __kvm_pgtable_visit(struct kvm_pgtable_walk_data *data,
>  	if (!kvm_pgtable_walk_continue(data->walker, ret))
>  		return ret;
>  
> -	if (!table) {
> +	if (!table || kvm_pgtable_skip_level(level + 1, ctx.flags)) {

[Severity: Medium]
Does this fail to skip the starting level of the page table walk if that
initial level matches the skip criteria?

Looking at __kvm_pgtable_visit() in arch/arm64/kvm/hyp/pgtable.c, the visitor
callbacks are executed unconditionally for the current level before we reach
this skip check:

	if (table && (ctx.flags & KVM_PGTABLE_WALK_TABLE_PRE)) {
		ret = kvm_pgtable_visitor_cb(data, &ctx, KVM_PGTABLE_WALK_TABLE_PRE);
		reload = true;
	}

	if (!table && (ctx.flags & KVM_PGTABLE_WALK_LEAF)) {
		ret = kvm_pgtable_visitor_cb(data, &ctx, KVM_PGTABLE_WALK_LEAF);
		reload = true;
	}

Since the skip condition here only evaluates level + 1 to prevent descending
further, if a caller begins a walk at a level that should be skipped (for
example, starting at level 2 with KVM_PGTABLE_WALK_SKIP_LEVEL2), the callbacks
for that root level will still execute. 

Should the current level also be checked against the skip flags before
executing the pre-table or leaf visitor callbacks?

>  		data->addr = ALIGN_DOWN(data->addr, kvm_granule_size(level));
>  		data->addr += kvm_granule_size(level);
>  		goto out;

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260708134101.2514759-1-leo.bras@arm.com?part=2