From: Paolo Bonzini <pbonzini@redhat.com>
To: Pankaj Gupta <pagupta@redhat.com>, Barret Rhoden <brho@google.com>
Cc: "Dan Williams" <dan.j.williams@intel.com>,
"David Hildenbrand" <david@redhat.com>,
"Dave Jiang" <dave.jiang@intel.com>,
"Ross Zwisler" <zwisler@kernel.org>,
"Vishal Verma" <vishal.l.verma@intel.com>,
"Radim Krčmář" <rkrcmar@redhat.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Ingo Molnar" <mingo@redhat.com>,
"Borislav Petkov" <bp@alien8.de>,
linux-nvdimm@lists.01.org, linux-kernel@vger.kernel.org,
"H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, kvm@vger.kernel.org,
"yu c zhang" <yu.c.zhang@intel.com>,
"yi z zhang" <yi.z.zhang@intel.com>
Subject: Re: [PATCH 2/2] kvm: Use huge pages for DAX-backed files
Date: Tue, 13 Nov 2018 13:41:20 +0100 [thread overview]
Message-ID: <74665f91-9803-88d0-7730-bbb9c7b84da1@redhat.com> (raw)
In-Reply-To: <286665658.33247363.1542103353780.JavaMail.zimbra@redhat.com>
On 13/11/2018 11:02, Pankaj Gupta wrote:
>
>>
>> On 09.11.18 21:39, Barret Rhoden wrote:
>>> This change allows KVM to map DAX-backed files made of huge pages with
>>> huge mappings in the EPT/TDP.
>>>
>>> DAX pages are not PageTransCompound. The existing check is trying to
>>> determine if the mapping for the pfn is a huge mapping or not. For
>>> non-DAX maps, e.g. hugetlbfs, that means checking PageTransCompound.
>>> For DAX, we can check the page table itself.
>>>
>>> Note that KVM already faulted in the page (or huge page) in the host's
>>> page table, and we hold the KVM mmu spinlock (grabbed before checking
>>> the mmu seq).
>>
>> I wonder if the KVM mmu spinlock is enough for walking (not KVM
>> exclusive) host page tables. Can you elaborate?
>
> As this patch is dependent on PageReserved patch(which is in progress), just
> wondering if we are able to test the code path for hugepage with DAX.
The MMU spinlock is taken in kvm_mmu_notifier_invalidate_range_end, so
it should be enough.
Paolo
>
> Thanks,
> Pankaj
>
>>
>>>
>>> Signed-off-by: Barret Rhoden <brho@google.com>
>>> ---
>>> arch/x86/kvm/mmu.c | 34 ++++++++++++++++++++++++++++++++--
>>> 1 file changed, 32 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
>>> index cf5f572f2305..2df8c459dc6a 100644
>>> --- a/arch/x86/kvm/mmu.c
>>> +++ b/arch/x86/kvm/mmu.c
>>> @@ -3152,6 +3152,36 @@ static int kvm_handle_bad_page(struct kvm_vcpu
>>> *vcpu, gfn_t gfn, kvm_pfn_t pfn)
>>> return -EFAULT;
>>> }
>>>
>>> +static bool pfn_is_huge_mapped(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn)
>>> +{
>>> + struct page *page = pfn_to_page(pfn);
>>> + unsigned long hva, map_shift;
>>> +
>>> + if (!is_zone_device_page(page))
>>> + return PageTransCompoundMap(page);
>>> +
>>> + /*
>>> + * DAX pages do not use compound pages. The page should have already
>>> + * been mapped into the host-side page table during try_async_pf(), so
>>> + * we can check the page tables directly.
>>> + */
>>> + hva = gfn_to_hva(kvm, gfn);
>>> + if (kvm_is_error_hva(hva))
>>> + return false;
>>> +
>>> + /*
>>> + * Our caller grabbed the KVM mmu_lock with a successful
>>> + * mmu_notifier_retry, so we're safe to walk the page table.
>>> + */
>>> + map_shift = dev_pagemap_mapping_shift(hva, current->mm);
>>
>> You could get rid of that local variable map_shift.
>>
>>> + switch (map_shift) {
>>> + case PMD_SHIFT:
>>> + case PUD_SIZE:
>>> + return true;
>>> + }
>>> + return false;
>>> +}
>>> +
>>> static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu,
>>> gfn_t *gfnp, kvm_pfn_t *pfnp,
>>> int *levelp)
>>> @@ -3168,7 +3198,7 @@ static void transparent_hugepage_adjust(struct
>>> kvm_vcpu *vcpu,
>>> */
>>> if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) &&
>>> level == PT_PAGE_TABLE_LEVEL &&
>>> - PageTransCompoundMap(pfn_to_page(pfn)) &&
>>> + pfn_is_huge_mapped(vcpu->kvm, gfn, pfn) &&
>>> !mmu_gfn_lpage_is_disallowed(vcpu, gfn, PT_DIRECTORY_LEVEL)) {
>>> unsigned long mask;
>>> /*
>>> @@ -5678,7 +5708,7 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm
>>> *kvm,
>>> */
>>> if (sp->role.direct &&
>>> !kvm_is_reserved_pfn(pfn) &&
>>> - PageTransCompoundMap(pfn_to_page(pfn))) {
>>> + pfn_is_huge_mapped(kvm, sp->gfn, pfn)) {
>>> pte_list_remove(rmap_head, sptep);
>>> need_tlb_flush = 1;
>>> goto restart;
>>>
>>
>> This looks surprisingly simple to me :)
>>
>> --
>>
>> Thanks,
>>
>> David / dhildenb
>>
next prev parent reply other threads:[~2018-11-13 12:41 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-09 20:39 [PATCH 0/2] kvm: Use huge pages for DAX-backed files Barret Rhoden
2018-11-09 20:39 ` [PATCH 1/2] mm: make dev_pagemap_mapping_shift() externally visible Barret Rhoden
2018-11-13 9:28 ` David Hildenbrand
2018-11-09 20:39 ` [PATCH 2/2] kvm: Use huge pages for DAX-backed files Barret Rhoden
2018-11-12 19:31 ` Paolo Bonzini
[not found] ` <861c4adb-e2f0-2caf-8f6e-9f09ecb0b624-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2018-11-13 16:21 ` Barret Rhoden
2018-11-13 18:22 ` Paolo Bonzini
2018-11-13 9:36 ` David Hildenbrand
2018-11-13 10:02 ` Pankaj Gupta
2018-11-13 12:41 ` Paolo Bonzini [this message]
[not found] ` <286665658.33247363.1542103353780.JavaMail.zimbra-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2018-11-13 15:56 ` Barret Rhoden
2018-11-14 9:09 ` Pankaj Gupta
[not found] ` <043a592d-6592-3053-15a0-68cc54a26deb-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2018-11-13 15:50 ` Barret Rhoden
[not found] ` <20181109203921.178363-1-brho-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2018-11-14 21:51 ` [PATCH v2 0/3] " Barret Rhoden
2018-11-14 21:51 ` [PATCH v2 1/3] mm: make dev_pagemap_mapping_shift() externally visible Barret Rhoden
2018-11-26 16:50 ` Paolo Bonzini
2018-11-26 18:32 ` Dan Williams
[not found] ` <20181114215155.259978-1-brho-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
2018-11-14 21:51 ` [PATCH v2 2/3] kvm: Use huge pages for DAX-backed files Barret Rhoden
2018-11-14 21:51 ` [PATCH v2 3/3] kvm: remove redundant PageReserved() check Barret Rhoden
2018-11-27 13:31 ` David Hildenbrand
2018-11-15 0:55 ` [PATCH v2 0/3] kvm: Use huge pages for DAX-backed files Dan Williams
2018-12-03 17:40 ` Barret Rhoden
2018-12-03 18:32 ` Alexander Duyck
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