Re: [PATCH v10 8/9] KVM: Handle page fault for private memory

Chao Peng
2022-12-12T07:28:35Z

On Fri, Dec 09, 2022 at 09:01:04AM +0000, Fuad Tabba wrote:
> Hi,
>
> On Fri, Dec 2, 2022 at 6:19 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> >
> > A KVM_MEM_PRIVATE memslot 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() 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@linux.intel.com>
> > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > ---
> > arch/x86/kvm/mmu/mmu.c | 63 +++++++++++++++++++++++++++++++--
> > arch/x86/kvm/mmu/mmu_internal.h | 14 +++++++-
> > arch/x86/kvm/mmu/mmutrace.h | 1 +
> > arch/x86/kvm/mmu/tdp_mmu.c | 2 +-
> > include/linux/kvm_host.h | 30 ++++++++++++++++
> > 5 files changed, 105 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index 2190fd8c95c0..b1953ebc012e 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -3058,7 +3058,7 @@ 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;
> > @@ -3070,6 +3070,9 @@ int kvm_mmu_max_mapping_level(struct kvm *kvm,
> > break;
> > }
> >
> > + if (is_private)
> > + return max_level;
> > +
> > if (max_level == PG_LEVEL_4K)
> > return PG_LEVEL_4K;
> >
> > @@ -3098,7 +3101,8 @@ 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;
> >
> > @@ -4178,6 +4182,49 @@ 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_do_memory_fault_exit(struct kvm_vcpu *vcpu,
> > + struct kvm_page_fault *fault)
> > +{
> > + 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.gpa = fault->gfn << PAGE_SHIFT;
>
> nit: As in previous patches, use helpers (for this and other similar
> shifts in this patch)?

Agreed.

>
> > + vcpu->run->memory.size = PAGE_SIZE;
> > + return RET_PF_USER;
> > +}
> > +
> > +static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu,
> > + struct kvm_page_fault *fault)
> > +{
> > + int order;
> > + struct kvm_memory_slot *slot = fault->slot;
> > +
> > + if (!kvm_slot_can_be_private(slot))
> > + return kvm_do_memory_fault_exit(vcpu, fault);
> > +
> > + 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;
> > @@ -4210,6 +4257,12 @@ static int kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
> > return RET_PF_EMULATE;
> > }
> >
> > + if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn))
> > + return kvm_do_memory_fault_exit(vcpu, fault);
> > +
> > + if (fault->is_private)
> > + return kvm_faultin_pfn_private(vcpu, fault);
> > +
> > async = false;
> > fault->pfn = __gfn_to_pfn_memslot(slot, fault->gfn, false, false, &async,
> > fault->write, &fault->map_writable,
> > @@ -5599,6 +5652,9 @@ 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)
> > @@ -6452,7 +6508,8 @@ 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 dbaf6755c5a7..5ccf08183b00 100644
> > --- a/arch/x86/kvm/mmu/mmu_internal.h
> > +++ b/arch/x86/kvm/mmu/mmu_internal.h
> > @@ -189,6 +189,7 @@ 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;
> >
> > /*
> > @@ -237,6 +238,7 @@ 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.
> > *
> > @@ -253,6 +255,7 @@ enum {
> > RET_PF_RETRY,
> > RET_PF_EMULATE,
> > RET_PF_INVALID,
> > + RET_PF_USER,
> > RET_PF_FIXED,
> > RET_PF_SPURIOUS,
> > };
> > @@ -310,7 +313,7 @@ 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);
> >
> > @@ -319,4 +322,13 @@ void *mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc);
> > void track_possible_nx_huge_page(struct kvm *kvm, struct kvm_mmu_page *sp);
> > void untrack_possible_nx_huge_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/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> > index 771210ce5181..8ba1a4afc546 100644
> > --- a/arch/x86/kvm/mmu/tdp_mmu.c
> > +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> > @@ -1768,7 +1768,7 @@ 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, false);
> > if (max_mapping_level < iter.level)
> > continue;
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index 25099c94e770..153842bb33df 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -2335,4 +2335,34 @@ static inline void kvm_arch_set_memory_attributes(struct kvm *kvm,
> > }
> > #endif /* __KVM_HAVE_ARCH_SET_MEMORY_ATTRIBUTES */
> >
> > +#ifdef CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES
> > +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> > +{
> > + return xa_to_value(xa_load(&kvm->mem_attr_array, gfn)) &
> > + KVM_MEMORY_ATTRIBUTE_PRIVATE;
> > +}
> > +#else
> > +static inline bool kvm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> > +{
> > + return false;
> > +}
> > +
> > +#endif /* CONFIG_HAVE_KVM_MEMORY_ATTRIBUTES */
> > +
> > +#ifdef 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)
> > +{
> > + int ret;
> > + struct page *page;
> > + pgoff_t index = gfn - slot->base_gfn +
> > + (slot->restricted_offset >> PAGE_SHIFT);
> > +
> > + ret = restrictedmem_get_page(slot->restricted_file, index,
> > + &page, order);
> > + *pfn = page_to_pfn(page);
> > + return ret;
> > +}
> > +#endif /* CONFIG_HAVE_KVM_RESTRICTED_MEM */
> > +
> > #endif
> > --
> > 2.25.1
> >
>
> With my limited understanding of x86 code:
> Reviewed-by: Fuad Tabba <tabba@google.com>
>
> The common code in kvm_host.h was used in the port to arm64, and the
> x86 fault handling code was used as a guide to how it should be done
> in pKVM (with similar code added there). So with these caveats in
> mind:
> Tested-by: Fuad Tabba <tabba@google.com>
>
> Cheers,
> /fuad