Re: [PATCH 7/9] KVM: arm64: Do not try to map PUDs when they are folded into PMD

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Hi Marc,

Noticed this patch while catching up with the lists.

Marc Zyngier <maz@xxxxxxxxxx> writes:

> For the obscure cases where PMD and PUD are the same size
> (64kB pages with 42bit VA, for example, which results in only
> two levels of page tables), we can't map anything as a PUD,
> because there is... erm... no PUD to speak of. Everything is
> either a PMD or a PTE.
>
> So let's only try and map a PUD when its size is different from
> that of a PMD.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: b8e0ba7c8bea ("KVM: arm64: Add support for creating PUD hugepages at stage 2")
> Reported-by: Gavin Shan <gshan@xxxxxxxxxx>
> Reported-by: Eric Auger <eric.auger@xxxxxxxxxx>
> Reviewed-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
> Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>
> Tested-by: Gavin Shan <gshan@xxxxxxxxxx>
> Tested-by: Eric Auger <eric.auger@xxxxxxxxxx>
> Tested-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> ---
>  arch/arm64/kvm/mmu.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 0121ef2c7c8d..16b8660ddbcc 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1964,7 +1964,12 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  		(fault_status == FSC_PERM &&
>  		 stage2_is_exec(mmu, fault_ipa, vma_pagesize));
>  
> -	if (vma_pagesize == PUD_SIZE) {
> +	/*
> +	 * If PUD_SIZE == PMD_SIZE, there is no real PUD level, and
> +	 * all we have is a 2-level page table. Trying to map a PUD in
> +	 * this case would be fatally wrong.
> +	 */
> +	if (PUD_SIZE != PMD_SIZE && vma_pagesize == PUD_SIZE) {
>  		pud_t new_pud = kvm_pfn_pud(pfn, mem_type);
>  
>  		new_pud = kvm_pud_mkhuge(new_pud);

Good catch!
Missed the 64kb / 42b VA case while adding the initial support.

Thanks for fixing it.

Punit



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