From: Gavin Shan <gshan@redhat.com>
To: Keqian Zhu <zhukeqian1@huawei.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
kvmarm@lists.cs.columbia.edu, Marc Zyngier <maz@kernel.org>
Cc: 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 17:52:58 +1000 [thread overview]
Message-ID: <960e097d-818b-00bc-b2ee-0da17857f862@redhat.com> (raw)
In-Reply-To: <20210415140328.24200-3-zhukeqian1@huawei.com>
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.
> + 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().
> static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> struct kvm_memory_slot *memslot, unsigned long hva,
> unsigned long fault_status)
> @@ -769,7 +798,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> return -EFAULT;
> }
>
> - /* Let's check if we will get back a huge page backed by hugetlbfs */
> + /*
> + * Let's check if we will get back a huge page backed by hugetlbfs, or
> + * get block mapping for device MMIO region.
> + */
> mmap_read_lock(current->mm);
> vma = find_vma_intersection(current->mm, hva, hva + 1);
> if (unlikely(!vma)) {
> @@ -778,15 +810,15 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> return -EFAULT;
> }
>
> - if (is_vm_hugetlb_page(vma))
> - vma_shift = huge_page_shift(hstate_vma(vma));
> - else
> - vma_shift = PAGE_SHIFT;
> -
> - if (logging_active ||
> - (vma->vm_flags & VM_PFNMAP)) {
> + /*
> + * logging_active is guaranteed to never be true for VM_PFNMAP
> + * memslots.
> + */
> + if (logging_active) {
> force_pte = true;
> vma_shift = PAGE_SHIFT;
> + } else {
> + vma_shift = get_vma_page_shift(vma, hva);
> }
>
> switch (vma_shift) {
> @@ -854,8 +886,17 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> return -EFAULT;
>
> if (kvm_is_device_pfn(pfn)) {
> + /*
> + * If the page was identified as device early by looking at
> + * the VMA flags, vma_pagesize is already representing the
> + * largest quantity we can map. If instead it was mapped
> + * via gfn_to_pfn_prot(), vma_pagesize is set to PAGE_SIZE
> + * and must not be upgraded.
> + *
> + * In both cases, we don't let transparent_hugepage_adjust()
> + * change things at the last minute.
> + */
> device = true;
> - force_pte = true;
> } else if (logging_active && !write_fault) {
> /*
> * Only actually map the page as writable if this was a write
> @@ -876,7 +917,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
> * If we are not forced to use page mapping, check if we are
> * backed by a THP and thus use block mapping if possible.
> */
> - if (vma_pagesize == PAGE_SIZE && !force_pte)
> + if (vma_pagesize == PAGE_SIZE && !(force_pte || device))
> vma_pagesize = transparent_hugepage_adjust(memslot, hva,
> &pfn, &fault_ipa);
> if (writable)
>
Thanks,
Gavin
next prev parent reply other threads:[~2021-04-21 5:53 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 [this message]
2021-04-21 6:36 ` Keqian Zhu
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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