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Date: Wed, 26 Oct 2022 14:54:25 -0700
From: Isaku Yamahata <isaku.yamahata@...il.com>
To: Chao Peng <chao.p.peng@...ux.intel.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
linux-doc@...r.kernel.org, qemu-devel@...gnu.org,
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>,
Shuah Khan <shuah@...nel.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>, tabba@...gle.com,
Michael Roth <michael.roth@....com>, mhocko@...e.com,
Muchun Song <songmuchun@...edance.com>, wei.w.wang@...el.com,
isaku.yamahata@...il.com
Subject: Re: [PATCH v9 7/8] KVM: Handle page fault for private memory
On Tue, Oct 25, 2022 at 11:13:43PM +0800,
Chao Peng <chao.p.peng@...ux.intel.com> wrote:
> A memslot with KVM_MEM_PRIVATE being set can include both fd-based
> private memory and hva-based shared memory. Architecture code (like TDX
> code) can tell whether the on-going fault is private or not. This patch
> adds a 'is_private' field to kvm_page_fault to indicate this and
> architecture code is expected to set it.
>
> To handle page fault for such memslot, the handling logic is different
> depending on whether the fault is private or shared. KVM checks if
> 'is_private' matches the host's view of the page (maintained in
> mem_attr_array).
> - For a successful match, private pfn is obtained with
> restrictedmem_get_page () 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
> in host's view and retry the fault.
>
> 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/mmu.c | 56 +++++++++++++++++++++++++++++++--
> arch/x86/kvm/mmu/mmu_internal.h | 14 ++++++++-
> arch/x86/kvm/mmu/mmutrace.h | 1 +
> arch/x86/kvm/mmu/spte.h | 6 ++++
> arch/x86/kvm/mmu/tdp_mmu.c | 3 +-
> include/linux/kvm_host.h | 28 +++++++++++++++++
> 6 files changed, 103 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 67a9823a8c35..10017a9f26ee 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -3030,7 +3030,7 @@ static int host_pfn_mapping_level(struct kvm *kvm, gfn_t gfn,
>
> int kvm_mmu_max_mapping_level(struct kvm *kvm,
> const struct kvm_memory_slot *slot, gfn_t gfn,
> - int max_level)
> + int max_level, bool is_private)
> {
> struct kvm_lpage_info *linfo;
> int host_level;
> @@ -3042,6 +3042,9 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm,
> break;
> }
>
> + if (is_private)
> + return max_level;
Below PG_LEVEL_NUM is passed by zap_collapsible_spte_range(). It doesn't make
sense.
> +
> if (max_level == PG_LEVEL_4K)
> return PG_LEVEL_4K;
>
> @@ -3070,7 +3073,8 @@ void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault
> * level, which will be used to do precise, accurate accounting.
> */
> fault->req_level = kvm_mmu_max_mapping_level(vcpu->kvm, slot,
> - fault->gfn, fault->max_level);
> + fault->gfn, fault->max_level,
> + fault->is_private);
> if (fault->req_level == PG_LEVEL_4K || fault->huge_page_disallowed)
> return;
>
> @@ -4141,6 +4145,32 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
> kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, 0, true);
> }
>
> +static inline u8 order_to_level(int order)
> +{
> + BUILD_BUG_ON(KVM_MAX_HUGEPAGE_LEVEL > PG_LEVEL_1G);
> +
> + if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_1G))
> + return PG_LEVEL_1G;
> +
> + if (order >= KVM_HPAGE_GFN_SHIFT(PG_LEVEL_2M))
> + return PG_LEVEL_2M;
> +
> + return PG_LEVEL_4K;
> +}
> +
> +static int kvm_faultin_pfn_private(struct kvm_page_fault *fault)
> +{
> + int order;
> + struct kvm_memory_slot *slot = fault->slot;
> +
> + if (kvm_restricted_mem_get_pfn(slot, fault->gfn, &fault->pfn, &order))
> + return RET_PF_RETRY;
> +
> + fault->max_level = min(order_to_level(order), fault->max_level);
> + fault->map_writable = !(slot->flags & KVM_MEM_READONLY);
> + return RET_PF_CONTINUE;
> +}
> +
> static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> {
> struct kvm_memory_slot *slot = fault->slot;
> @@ -4173,6 +4203,22 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> return RET_PF_EMULATE;
> }
>
> + if (kvm_slot_can_be_private(slot) &&
> + fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn)) {
> + vcpu->run->exit_reason = KVM_EXIT_MEMORY_FAULT;
> + if (fault->is_private)
> + vcpu->run->memory.flags = KVM_MEMORY_EXIT_FLAG_PRIVATE;
> + else
> + vcpu->run->memory.flags = 0;
> + vcpu->run->memory.padding = 0;
> + vcpu->run->memory.gpa = fault->gfn << PAGE_SHIFT;
> + vcpu->run->memory.size = PAGE_SIZE;
> + return RET_PF_USER;
> + }
> +
> + if (fault->is_private)
> + return kvm_faultin_pfn_private(fault);
> +
> async = false;
> fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, &async,
> fault->write, &fault->map_writable,
> @@ -5557,6 +5603,9 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
> return -EIO;
> }
>
> + if (r == RET_PF_USER)
> + return 0;
> +
> if (r < 0)
> return r;
> if (r != RET_PF_EMULATE)
> @@ -6408,7 +6457,8 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm,
> */
> if (sp->role.direct &&
> sp->role.level < kvm_mmu_max_mapping_level(kvm, slot, sp->gfn,
> - PG_LEVEL_NUM)) {
> + PG_LEVEL_NUM,
> + false)) {
> kvm_zap_one_rmap_spte(kvm, rmap_head, sptep);
>
> if (kvm_available_flush_tlb_with_range())
> diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> index 582def531d4d..5cdff5ca546c 100644
> --- a/arch/x86/kvm/mmu/mmu_internal.h
> +++ b/arch/x86/kvm/mmu/mmu_internal.h
> @@ -188,6 +188,7 @@ 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;
>
> /*
> @@ -236,6 +237,7 @@ int kvm_tdp_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
> * RET_PF_RETRY: let CPU fault again on the address.
> * RET_PF_EMULATE: mmio page fault, emulate the instruction directly.
> * RET_PF_INVALID: the spte is invalid, let the real page fault path update it.
> + * RET_PF_USER: need to exit to userspace to handle this fault.
> * RET_PF_FIXED: The faulting entry has been fixed.
> * RET_PF_SPURIOUS: The faulting entry was already fixed, e.g. by another vCPU.
> *
> @@ -252,6 +254,7 @@ enum {
> RET_PF_RETRY,
> RET_PF_EMULATE,
> RET_PF_INVALID,
> + RET_PF_USER,
> RET_PF_FIXED,
> RET_PF_SPURIOUS,
> };
> @@ -309,7 +312,7 @@ static inline int kvm_mmu_do_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>
> int kvm_mmu_max_mapping_level(struct kvm *kvm,
> const struct kvm_memory_slot *slot, gfn_t gfn,
> - int max_level);
> + int max_level, bool is_private);
> void kvm_mmu_hugepage_adjust(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault);
> void disallowed_hugepage_adjust(struct kvm_page_fault *fault, u64 spte, int cur_level);
>
> @@ -318,4 +321,13 @@ void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
> void account_huge_nx_page(struct kvm *kvm, struct kvm_mmu_page *sp);
> void unaccount_huge_nx_page(struct kvm *kvm, struct kvm_mmu_page *sp);
>
> +#ifndef CONFIG_HAVE_KVM_RESTRICTED_MEM
> +static inline int kvm_restricted_mem_get_pfn(struct kvm_memory_slot *slot,
> + gfn_t gfn, kvm_pfn_t *pfn, int *order)
> +{
> + WARN_ON_ONCE(1);
> + return -EOPNOTSUPP;
> +}
> +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> +
> #endif /* __KVM_X86_MMU_INTERNAL_H */
> diff --git a/arch/x86/kvm/mmu/mmutrace.h b/arch/x86/kvm/mmu/mmutrace.h
> index ae86820cef69..2d7555381955 100644
> --- a/arch/x86/kvm/mmu/mmutrace.h
> +++ b/arch/x86/kvm/mmu/mmutrace.h
> @@ -58,6 +58,7 @@ TRACE_DEFINE_ENUM(RET_PF_CONTINUE);
> TRACE_DEFINE_ENUM(RET_PF_RETRY);
> TRACE_DEFINE_ENUM(RET_PF_EMULATE);
> TRACE_DEFINE_ENUM(RET_PF_INVALID);
> +TRACE_DEFINE_ENUM(RET_PF_USER);
> TRACE_DEFINE_ENUM(RET_PF_FIXED);
> TRACE_DEFINE_ENUM(RET_PF_SPURIOUS);
>
> diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
> index 7670c13ce251..9acdf72537ce 100644
> --- a/arch/x86/kvm/mmu/spte.h
> +++ b/arch/x86/kvm/mmu/spte.h
> @@ -315,6 +315,12 @@ static inline bool is_dirty_spte(u64 spte)
> return dirty_mask ? spte & dirty_mask : spte & PT_WRITABLE_MASK;
> }
>
> +static inline bool is_private_spte(u64 spte)
> +{
> + /* FIXME: Query C-bit/S-bit for SEV/TDX. */
> + return false;
> +}
> +
PFN encoded in spte doesn't make sense. In VMM for TDX, private-vs-shared is
determined by S-bit of GFN.
> static inline u64 get_rsvd_bits(struct rsvd_bits_validate *rsvd_check, u64 pte,
> int level)
> {
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 672f0432d777..9f97aac90606 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -1768,7 +1768,8 @@ static void zap_collapsible_spte_range(struct kvm *kvm,
> continue;
>
> max_mapping_level = kvm_mmu_max_mapping_level(kvm, slot,
> - iter.gfn, PG_LEVEL_NUM);
> + iter.gfn, PG_LEVEL_NUM,
> + is_private_spte(iter.old_spte));
> if (max_mapping_level < iter.level)
> continue;
This is to merge pages into a large page on the next kvm page fault. large page
support is not yet supported. Let's skip the private slot until large page
support is done.
--
Isaku Yamahata <isaku.yamahata@...il.com>
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