From: Gavin Shan <gshan@redhat.com>
To: Marc Zyngier <maz@kernel.org>
Cc: will@kernel.org, kvmarm@lists.cs.columbia.edu,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 3/3] KVM: arm64: Failback on unsupported huge page sizes
Date: Mon, 26 Oct 2020 10:04:08 +1100 [thread overview]
Message-ID: <74539016-f41f-c6a0-5c37-034204dc00cc@redhat.com> (raw)
In-Reply-To: <87y2juoa2s.wl-maz@kernel.org>
Hi Marc,
On 10/25/20 9:48 PM, Marc Zyngier wrote:
> On Sun, 25 Oct 2020 01:27:39 +0100,
> Gavin Shan <gshan@redhat.com> wrote:
>>
>> The huge page could be mapped through multiple contiguous PMDs or PTEs.
>> The corresponding huge page sizes aren't supported by the page table
>> walker currently.
>>
>> This fails the unsupported huge page sizes to the near one. Otherwise,
>> the guest can't boot successfully: CONT_PMD_SHIFT and CONT_PTE_SHIFT
>> fail back to PMD_SHIFT and PAGE_SHIFT separately.
>>
>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>> ---
>> arch/arm64/kvm/mmu.c | 8 ++++++++
>> 1 file changed, 8 insertions(+)
>>
>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>> index 0f51585adc04..81cbdc368246 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -793,12 +793,20 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>> vma_shift = PMD_SHIFT;
>> #endif
>>
>> + if (vma_shift == CONT_PMD_SHIFT)
>> + vma_shift = PMD_SHIFT;
>> +
>> if (vma_shift == PMD_SHIFT &&
>> !fault_supports_stage2_huge_mapping(memslot, hva, PMD_SIZE)) {
>> force_pte = true;
>> vma_shift = PAGE_SHIFT;
>> }
>>
>> + if (vma_shift == CONT_PTE_SHIFT) {
>> + force_pte = true;
>> + vma_shift = PAGE_SHIFT;
>> + }
>> +
>> vma_pagesize = 1UL << vma_shift;
>> if (vma_pagesize == PMD_SIZE || vma_pagesize == PUD_SIZE)
>> fault_ipa &= ~(vma_pagesize - 1);
>
> Yup, nice catch. However, I think we should take this opportunity to
> rationalise the logic here, and catch future discrepancies (should
> someone add contiguous PUD or something similarly silly). How about
> something like this (untested):
>
Yeah, I started the work to support contiguous PMDs/PTEs, but I'm not
sure when I can post the patches for review as my time becomes a bit
fragmented recently. At least, I need focus on "async page fault" in
the coming weeks :)
Thanks for the suggested code and it worked for me. I'll post v2 to
integrate them. However, I would like to drop PATCH[1] and PATCH[2]
as I really don't have strong reasons to have them.
Thanks,
Gavin
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index cc323d96c9d4..d9a13a8a82e0 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -787,14 +787,31 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> vma_shift = PAGE_SHIFT;
> }
>
> - if (vma_shift == PUD_SHIFT &&
> - !fault_supports_stage2_huge_mapping(memslot, hva, PUD_SIZE))
> - vma_shift = PMD_SHIFT;
> + switch (vma_shift) {
> + case PUD_SHIFT:
> + if (fault_supports_stage2_huge_mapping(memslot, hva, PUD_SIZE))
> + break;
> + fallthrough;
>
> - if (vma_shift == PMD_SHIFT &&
> - !fault_supports_stage2_huge_mapping(memslot, hva, PMD_SIZE)) {
> - force_pte = true;
> + case CONT_PMD_SHIFT:
> + vma_shift = PMD_SHIFT;
> + fallthrough;
> +
> + case PMD_SHIFT:
> + if (fault_supports_stage2_huge_mapping(memslot, hva, PMD_SIZE))
> + break;
> + fallthrough;
> +
> + case CONT_PTE_SHIFT:
> vma_shift = PAGE_SHIFT;
> + force_pte = true;
> + fallthrough;
> +
> + case PAGE_SHIFT:
> + break;
> +
> + default:
> + WARN_ONCE(1, "Unknown vma_shift %d", vma_shift);
> }
>
> vma_pagesize = 1UL << vma_shift;
>
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next prev parent reply other threads:[~2020-10-25 23:04 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-25 0:27 [PATCH 0/3] KVM: arm64: Failback on unsupported huge pages Gavin Shan
2020-10-25 0:27 ` [PATCH 1/3] KVM: arm64: Check if 52-bits PA is enabled Gavin Shan
2020-10-25 9:52 ` Marc Zyngier
2020-10-25 22:23 ` Gavin Shan
2020-10-26 8:40 ` Will Deacon
2020-10-26 8:53 ` Marc Zyngier
2020-10-26 22:48 ` Gavin Shan
2020-10-25 0:27 ` [PATCH 2/3] KVM: arm64: Don't map PUD huge page if it's not available Gavin Shan
2020-10-25 10:05 ` Marc Zyngier
2020-10-25 22:27 ` Gavin Shan
2020-10-25 0:27 ` [PATCH 3/3] KVM: arm64: Failback on unsupported huge page sizes Gavin Shan
2020-10-25 10:48 ` Marc Zyngier
2020-10-25 23:04 ` Gavin Shan [this message]
2020-10-26 8:55 ` Marc Zyngier
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