Re: [PATCH v2 2/2] KVM: arm64: ptdump: Flush the last region

[Dev Jain]

On 25/07/26 12:24 am, Wei-Lin Chang wrote:
> Currently the stage-2 ptdump calls note_page() at each leaf entry visit.
> This simply misses the output of the last region, because note_page()
> only dumps output when it detects a change in level/prot, or when the
> walk enters a next marker section. The last region in the guest IPA
> space with the same level/prot is not dumped since there is no change
> after it.
> 
> Call note_page_flush() to dump the final region. note_page_flush()
> expects ptdump_state.range[] to be initialized to the range of the
> address space, so also do that.
> 
> Also change the second marker's start address to ULONG_MAX so we never
> cross it. This avoids dumping redundant marker names (which are NULL),
> and advancing beyond the end of the marker array.
> 
> Fixes: 7c4f73548ed1 ("KVM: arm64: Register ptdump with debugfs on guest creation")
> Reported-by: Sashiko AI <sashiko-bot@xxxxxxxxxx>
> Closes: https://lore.kernel.org/kvmarm/20260630122758.891011F00A3A@xxxxxxxxxxxxxxx/
> Signed-off-by: Wei-Lin Chang <weilin.chang@xxxxxxx>
> ---
>  arch/arm64/kvm/ptdump.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kvm/ptdump.c b/arch/arm64/kvm/ptdump.c
> index c9140e22abcf..222577163d2b 100644
> --- a/arch/arm64/kvm/ptdump.c
> +++ b/arch/arm64/kvm/ptdump.c
> @@ -130,7 +130,7 @@ static struct kvm_ptdump_guest_state *kvm_ptdump_parser_create(struct kvm_s2_mmu
>  	}
>  
>  	st->ipa_marker[0].name		= "Guest IPA";
> -	st->ipa_marker[1].start_address = BIT(pgtable->ia_bits);
> +	st->ipa_marker[1].start_address = ULONG_MAX;
>  
>  	st->mmu				= mmu;
>  	return st;
> @@ -148,18 +148,26 @@ static int kvm_ptdump_guest_show(struct seq_file *m, void *unused)
>  		.flags	= KVM_PGTABLE_WALK_LEAF,
>  	};
>  
> +	guard(write_lock)(&kvm->mmu_lock);
>  	st->parser_state = (struct ptdump_pg_state) {
>  		.marker		= &st->ipa_marker[0],
>  		.level		= -1,
>  		.pg_level	= &st->level[0],
>  		.seq		= m,
> +		.ptdump		= {
> +			.range = (struct ptdump_range[]){
> +				{0, BIT(mmu->pgt->ia_bits)},
> +				{0, 0}
> +			}

I am having a real hard time reading that indentation :) you
could make it look like what we have currently in ptdump_walk().

The code looks sensible to me. I have also tested by booting a
Linux VM inside a Linux VM on a Mac, and I see the stage2 ptdump
prints the last range upto the ia_bits correctly. So with the
nit addressed above:

Reviewed-by: Dev Jain <dev.jain@xxxxxxx>
Tested-by: Dev Jain <dev.jain@xxxxxxx>




> +		}
>  	};
>  
> -	write_lock(&kvm->mmu_lock);
>  	ret = kvm_pgtable_walk(mmu->pgt, 0, BIT(mmu->pgt->ia_bits), &walker);
> -	write_unlock(&kvm->mmu_lock);
> +	if (ret)
> +		return ret;
> +	note_page_flush(&st->parser_state.ptdump);
>  
> -	return ret;
> +	return 0;
>  }
>  
>  static int kvm_ptdump_guest_open(struct inode *m, struct file *file)