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Message-ID: <b3ce0855-0e4b-782a-599c-26590df948dd@amd.com>
Date: Fri, 24 Jun 2022 09:28:23 +0530
From: "Nikunj A. Dadhania" <nikunj@....com>
To: Chao Peng <chao.p.peng@...ux.intel.com>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
linux-doc@...r.kernel.org, qemu-devel@...gnu.org
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Jonathan Corbet <corbet@....net>,
Sean Christopherson <seanjc@...gle.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
Hugh Dickins <hughd@...gle.com>,
Jeff Layton <jlayton@...nel.org>,
"J . Bruce Fields" <bfields@...ldses.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Mike Rapoport <rppt@...nel.org>,
Steven Price <steven.price@....com>,
"Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
Vlastimil Babka <vbabka@...e.cz>,
Vishal Annapurve <vannapurve@...gle.com>,
Yu Zhang <yu.c.zhang@...ux.intel.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
luto@...nel.org, jun.nakajima@...el.com, dave.hansen@...el.com,
ak@...ux.intel.com, david@...hat.com, aarcange@...hat.com,
ddutile@...hat.com, dhildenb@...hat.com,
Quentin Perret <qperret@...gle.com>,
Michael Roth <michael.roth@....com>, mhocko@...e.com
Subject: Re: [PATCH v6 6/8] KVM: Handle page fault for private memory
On 5/19/2022 9:07 PM, Chao Peng wrote:
> A page fault can carry the information of whether the access if private
> or not for KVM_MEM_PRIVATE memslot, this can be filled by architecture
> code(like TDX code). To handle page faut for such access, KVM maps the
> page only when this private property matches host's view on this page
> which can be decided by checking whether the corresponding page is
> populated in the private fd or not. A page is considered as private when
> the page is populated in the private fd, otherwise it's shared.
>
> For a successful match, private pfn is obtained with memfile_notifier
> callbacks from private fd and shared pfn is obtained with existing
> get_user_pages.
>
> For a failed match, KVM causes a KVM_EXIT_MEMORY_FAULT exit to
> userspace. Userspace then can convert memory between private/shared from
> host's view then retry the access.
>
> Co-developed-by: Yu Zhang <yu.c.zhang@...ux.intel.com>
> Signed-off-by: Yu Zhang <yu.c.zhang@...ux.intel.com>
> Signed-off-by: Chao Peng <chao.p.peng@...ux.intel.com>
> ---
> arch/x86/kvm/mmu.h | 1 +
> arch/x86/kvm/mmu/mmu.c | 70 +++++++++++++++++++++++++++++++--
> arch/x86/kvm/mmu/mmu_internal.h | 17 ++++++++
> arch/x86/kvm/mmu/mmutrace.h | 1 +
> arch/x86/kvm/mmu/paging_tmpl.h | 5 ++-
> include/linux/kvm_host.h | 22 +++++++++++
> 6 files changed, 112 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
> index 7e258cc94152..c84835762249 100644
> --- a/arch/x86/kvm/mmu.h
> +++ b/arch/x86/kvm/mmu.h
> @@ -176,6 +176,7 @@ struct kvm_page_fault {
>
> /* Derived from mmu and global state. */
> const bool is_tdp;
> + const bool is_private;
> const bool nx_huge_page_workaround_enabled;
>
> /*
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index afe18d70ece7..e18460e0d743 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2899,6 +2899,9 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm,
> if (max_level == PG_LEVEL_4K)
> return PG_LEVEL_4K;
>
> + if (kvm_slot_is_private(slot))
> + return max_level;
Can you explain the rationale behind the above change?
AFAIU, this overrides the transparent_hugepage=never setting for both
shared and private mappings.
> host_level = host_pfn_mapping_level(kvm, gfn, pfn, slot);
> return min(host_level, max_level);
> }
Regards
Nikunj
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