From: Keqian Zhu <zhukeqian1@huawei.com>
To: Gavin Shan <gshan@redhat.com>, <linux-kernel@vger.kernel.org>,
<linux-arm-kernel@lists.infradead.org>, <kvm@vger.kernel.org>,
<kvmarm@lists.cs.columbia.edu>
Cc: Marc Zyngier <maz@kernel.org>, <wanghaibin.wang@huawei.com>
Subject: Re: [PATCH v4 2/2] kvm/arm64: Try stage2 block mapping for host device MMIO
Date: Wed, 21 Apr 2021 14:36:55 +0800 [thread overview]
Message-ID: <105a403a-e48b-15bc-44ff-0ff34f7d2194@huawei.com> (raw)
In-Reply-To: <960e097d-818b-00bc-b2ee-0da17857f862@redhat.com>
On 2021/4/21 15:52, Gavin Shan wrote:
> Hi Keqian,
>
> On 4/16/21 12:03 AM, Keqian Zhu wrote:
>> The MMIO region of a device maybe huge (GB level), try to use
>> block mapping in stage2 to speedup both map and unmap.
>>
>> Compared to normal memory mapping, we should consider two more
>> points when try block mapping for MMIO region:
>>
>> 1. For normal memory mapping, the PA(host physical address) and
>> HVA have same alignment within PUD_SIZE or PMD_SIZE when we use
>> the HVA to request hugepage, so we don't need to consider PA
>> alignment when verifing block mapping. But for device memory
>> mapping, the PA and HVA may have different alignment.
>>
>> 2. For normal memory mapping, we are sure hugepage size properly
>> fit into vma, so we don't check whether the mapping size exceeds
>> the boundary of vma. But for device memory mapping, we should pay
>> attention to this.
>>
>> This adds get_vma_page_shift() to get page shift for both normal
>> memory and device MMIO region, and check these two points when
>> selecting block mapping size for MMIO region.
>>
>> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
>> ---
>> arch/arm64/kvm/mmu.c | 61 ++++++++++++++++++++++++++++++++++++--------
>> 1 file changed, 51 insertions(+), 10 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>> index c59af5ca01b0..5a1cc7751e6d 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -738,6 +738,35 @@ transparent_hugepage_adjust(struct kvm_memory_slot *memslot,
>> return PAGE_SIZE;
>> }
>> +static int get_vma_page_shift(struct vm_area_struct *vma, unsigned long hva)
>> +{
>> + unsigned long pa;
>> +
>> + if (is_vm_hugetlb_page(vma) && !(vma->vm_flags & VM_PFNMAP))
>> + return huge_page_shift(hstate_vma(vma));
>> +
>> + if (!(vma->vm_flags & VM_PFNMAP))
>> + return PAGE_SHIFT;
>> +
>> + VM_BUG_ON(is_vm_hugetlb_page(vma));
>> +
>
> I don't understand how VM_PFNMAP is set for hugetlbfs related vma.
> I think they are exclusive, meaning the flag is never set for
> hugetlbfs vma. If it's true, VM_PFNMAP needn't be checked on hugetlbfs
> vma and the VM_BUG_ON() becomes unnecessary.
Yes, but we're not sure all drivers follow this rule. Add a BUG_ON() is
a way to catch issue.
>
>> + pa = (vma->vm_pgoff << PAGE_SHIFT) + (hva - vma->vm_start);
>> +
>> +#ifndef __PAGETABLE_PMD_FOLDED
>> + if ((hva & (PUD_SIZE - 1)) == (pa & (PUD_SIZE - 1)) &&
>> + ALIGN_DOWN(hva, PUD_SIZE) >= vma->vm_start &&
>> + ALIGN(hva, PUD_SIZE) <= vma->vm_end)
>> + return PUD_SHIFT;
>> +#endif
>> +
>> + if ((hva & (PMD_SIZE - 1)) == (pa & (PMD_SIZE - 1)) &&
>> + ALIGN_DOWN(hva, PMD_SIZE) >= vma->vm_start &&
>> + ALIGN(hva, PMD_SIZE) <= vma->vm_end)
>> + return PMD_SHIFT;
>> +
>> + return PAGE_SHIFT;
>> +}
>> +
>
> There is "switch(...)" fallback mechanism in user_mem_abort(). PUD_SIZE/PMD_SIZE
> can be downgraded accordingly if the addresses fails in the alignment check
> by fault_supports_stage2_huge_mapping(). I think it would make user_mem_abort()
> simplified if the logic can be moved to get_vma_page_shift().
>
> Another question if we need the check from fault_supports_stage2_huge_mapping()
> if VM_PFNMAP area is going to be covered by block mapping. If so, the "switch(...)"
> fallback mechanism needs to be part of get_vma_page_shift().
Yes, Good suggestion. My idea is that we can keep this series simpler and do further
optimization in another patch series. Do you mind to send a patch?
Thanks,
Keqian
next prev parent reply other threads:[~2021-04-21 6:37 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-15 14:03 [PATCH v4 0/2] kvm/arm64: Try stage2 block mapping for host device MMIO Keqian Zhu
2021-04-15 14:03 ` [PATCH v4 1/2] kvm/arm64: Remove the creation time's mapping of MMIO regions Keqian Zhu
2021-04-21 6:38 ` Gavin Shan
2021-04-21 6:28 ` Keqian Zhu
2021-04-22 2:12 ` Gavin Shan
2021-04-22 7:41 ` Keqian Zhu
2021-04-23 1:35 ` Gavin Shan
2021-04-23 1:36 ` Keqian Zhu
2021-04-23 0:36 ` Gavin Shan
2021-04-15 14:03 ` [PATCH v4 2/2] kvm/arm64: Try stage2 block mapping for host device MMIO Keqian Zhu
2021-04-15 14:08 ` Keqian Zhu
2021-04-16 14:44 ` Marc Zyngier
2021-04-17 1:05 ` Keqian Zhu
2021-04-21 7:52 ` Gavin Shan
2021-04-21 6:36 ` Keqian Zhu [this message]
2021-04-22 2:25 ` Gavin Shan
2021-04-22 6:51 ` Marc Zyngier
2021-04-23 0:42 ` Gavin Shan
2021-04-23 0:37 ` Gavin Shan
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