Messages in this thread Patch in this message | | | Date | Fri, 15 May 2015 23:32:16 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH 12/13] KVM: x86: add KVM_MEM_X86_SMRAM memory slot flag |
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On 04/30/2015 02:36 PM, Paolo Bonzini wrote: > This adds an arch-specific memslot flag that hides slots unless the > VCPU is in system management mode. > > Some care is needed in order to limit the overhead of x86_gfn_to_memslot > when compared with gfn_to_memslot. Thankfully, we have __gfn_to_memslot > and search_memslots which are the same, so we can add some extra output > to search_memslots. The compiler will optimize it as dead code in > __gfn_to_memslot, and will use it to thread jumps in x86_gfn_to_memslot. > > > struct kvm_memory_slot *x86_gfn_to_memslot(struct kvm_vcpu *vcpu, gfn_t gfn) > { > - struct kvm_memory_slot *slot = gfn_to_memslot(vcpu->kvm, gfn); > + /* By using search_memslots directly the compiler can optimize away > + * the "if (found)" check below. > + * > + * It cannot do the same for gfn_to_memslot because it is not inlined, > + * and it also cannot do the same for __gfn_to_memslot because the > + * kernel is compiled with -fno-delete-null-pointer-checks. > + */ > + bool found; > + struct kvm_memslots *memslots = kvm_memslots(vcpu->kvm); > + struct kvm_memory_slot *slot = search_memslots(memslots, gfn, &found); > + > + if (found && unlikely(slot->flags & KVM_MEM_X86_SMRAM) && !is_smm(vcpu)) > + return NULL; >
Alternative approach: store the memslot pointer in the vcpu, instead of of vcpu->kvm. The uapi interface code can generate two memslot tables to be stored in kvm->, one for smm and one for !smm.
This is a little more generic and can be used for other asymmetric memory maps causes (the only one I can think of, mapping the APIC to different physical addresses, can't be efficiently supported).
> return slot; > } > @@ -112,7 +125,15 @@ EXPORT_SYMBOL_GPL(x86_read_guest); > int x86_gfn_to_hva_cache_init(struct kvm *kvm, struct gfn_to_hva_cache *ghc, > gpa_t gpa, unsigned long len) > { > - return kvm_gfn_to_hva_cache_init(kvm, ghc, gpa, len); > + int r = kvm_gfn_to_hva_cache_init(kvm, ghc, gpa, len); > + > + if (r < 0) > + return r; > + > + /* Use slow path for reads and writes to SMRAM. */ > + if (ghc->memslot && (ghc->memslot->flags & KVM_MEM_X86_SMRAM)) > + ghc->memslot = NULL; > + return r; > } > EXPORT_SYMBOL_GPL(x86_gfn_to_hva_cache_init); > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index e7cfee09970a..ea3db5d89f67 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -800,16 +800,18 @@ static inline void kvm_guest_exit(void) > * gfn_to_memslot() itself isn't here as an inline because that would > * bloat other code too much. > */ > -static inline struct kvm_memory_slot * > -search_memslots(struct kvm_memslots *slots, gfn_t gfn) > +static __always_inline struct kvm_memory_slot * > +search_memslots(struct kvm_memslots *slots, gfn_t gfn, bool *found) > { > int start = 0, end = slots->used_slots; > int slot = atomic_read(&slots->lru_slot); > struct kvm_memory_slot *memslots = slots->memslots; > > if (gfn >= memslots[slot].base_gfn && > - gfn < memslots[slot].base_gfn + memslots[slot].npages) > + gfn < memslots[slot].base_gfn + memslots[slot].npages) { > + *found = true; > return &memslots[slot]; > + } > > while (start < end) { > slot = start + (end - start) / 2; > @@ -823,16 +825,20 @@ search_memslots(struct kvm_memslots *slots, gfn_t gfn) > if (gfn >= memslots[start].base_gfn && > gfn < memslots[start].base_gfn + memslots[start].npages) { > atomic_set(&slots->lru_slot, start); > + *found = true; > return &memslots[start]; > } > > + *found = false; > return NULL; > } > > static inline struct kvm_memory_slot * > __gfn_to_memslot(struct kvm_memslots *slots, gfn_t gfn) > { > - return search_memslots(slots, gfn); > + bool found; > + > + return search_memslots(slots, gfn, &found); > } > > static inline unsigned long > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index e82c46b9860f..b8b76106a003 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -716,6 +716,10 @@ static int check_memory_region_flags(struct kvm_userspace_memory_region *mem) > #ifdef __KVM_HAVE_READONLY_MEM > valid_flags |= KVM_MEM_READONLY; > #endif > +#ifdef __KVM_ARCH_VALID_FLAGS > + BUILD_BUG_ON(__KVM_ARCH_VALID_FLAGS & KVM_MEMSLOT_INVALID); > + valid_flags |= __KVM_ARCH_VALID_FLAGS; > +#endif > > if (mem->flags & ~valid_flags) > return -EINVAL;
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