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Shutemov" To: Vitaly Kuznetsov Cc: David Rientjes , Andrea Arcangeli , Kees Cook , Will Drewry , "Edgecombe, Rick P" , "Kleen, Andi" , x86@kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Paolo Bonzini , Sean Christopherson , Wanpeng Li , Jim Mattson , Joerg Roedel Subject: Re: [RFC 06/16] KVM: Use GUP instead of copy_from/to_user() to access guest memory Message-ID: <20200525151755.yzbmemtrii455s6k@box> References: <20200522125214.31348-1-kirill.shutemov@linux.intel.com> <20200522125214.31348-7-kirill.shutemov@linux.intel.com> <87a71w832c.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87a71w832c.fsf@vitty.brq.redhat.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 25, 2020 at 05:08:43PM +0200, Vitaly Kuznetsov wrote: > "Kirill A. Shutemov" writes: > > > New helpers copy_from_guest()/copy_to_guest() to be used if KVM memory > > protection feature is enabled. > > > > Signed-off-by: Kirill A. Shutemov > > --- > > include/linux/kvm_host.h | 4 +++ > > virt/kvm/kvm_main.c | 78 ++++++++++++++++++++++++++++++++++------ > > 2 files changed, 72 insertions(+), 10 deletions(-) > > > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > > index 131cc1527d68..bd0bb600f610 100644 > > --- a/include/linux/kvm_host.h > > +++ b/include/linux/kvm_host.h > > @@ -503,6 +503,7 @@ struct kvm { > > struct srcu_struct srcu; > > struct srcu_struct irq_srcu; > > pid_t userspace_pid; > > + bool mem_protected; > > }; > > > > #define kvm_err(fmt, ...) \ > > @@ -727,6 +728,9 @@ void kvm_set_pfn_dirty(kvm_pfn_t pfn); > > void kvm_set_pfn_accessed(kvm_pfn_t pfn); > > void kvm_get_pfn(kvm_pfn_t pfn); > > > > +int copy_from_guest(void *data, unsigned long hva, int len); > > +int copy_to_guest(unsigned long hva, const void *data, int len); > > + > > void kvm_release_pfn(kvm_pfn_t pfn, bool dirty, struct gfn_to_pfn_cache *cache); > > int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset, > > int len); > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > > index 731c1e517716..033471f71dae 100644 > > --- a/virt/kvm/kvm_main.c > > +++ b/virt/kvm/kvm_main.c > > @@ -2248,8 +2248,48 @@ static int next_segment(unsigned long len, int offset) > > return len; > > } > > > > +int copy_from_guest(void *data, unsigned long hva, int len) > > +{ > > + int offset = offset_in_page(hva); > > + struct page *page; > > + int npages, seg; > > + > > + while ((seg = next_segment(len, offset)) != 0) { > > + npages = get_user_pages_unlocked(hva, 1, &page, 0); > > + if (npages != 1) > > + return -EFAULT; > > + memcpy(data, page_address(page) + offset, seg); > > + put_page(page); > > + len -= seg; > > + hva += seg; > > + offset = 0; > > + } > > + > > + return 0; > > +} > > + > > +int copy_to_guest(unsigned long hva, const void *data, int len) > > +{ > > + int offset = offset_in_page(hva); > > + struct page *page; > > + int npages, seg; > > + > > + while ((seg = next_segment(len, offset)) != 0) { > > + npages = get_user_pages_unlocked(hva, 1, &page, FOLL_WRITE); > > + if (npages != 1) > > + return -EFAULT; > > + memcpy(page_address(page) + offset, data, seg); > > + put_page(page); > > + len -= seg; > > + hva += seg; > > + offset = 0; > > + } > > + return 0; > > +} > > + > > static int __kvm_read_guest_page(struct kvm_memory_slot *slot, gfn_t gfn, > > - void *data, int offset, int len) > > + void *data, int offset, int len, > > + bool protected) > > { > > int r; > > unsigned long addr; > > @@ -2257,7 +2297,10 @@ static int __kvm_read_guest_page(struct kvm_memory_slot *slot, gfn_t gfn, > > addr = gfn_to_hva_memslot_prot(slot, gfn, NULL); > > if (kvm_is_error_hva(addr)) > > return -EFAULT; > > - r = __copy_from_user(data, (void __user *)addr + offset, len); > > + if (protected) > > + r = copy_from_guest(data, addr + offset, len); > > + else > > + r = __copy_from_user(data, (void __user *)addr + offset, len); > > if (r) > > return -EFAULT; > > return 0; > > @@ -2268,7 +2311,8 @@ int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset, > > { > > struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn); > > > > - return __kvm_read_guest_page(slot, gfn, data, offset, len); > > + return __kvm_read_guest_page(slot, gfn, data, offset, len, > > + kvm->mem_protected); > > } > > EXPORT_SYMBOL_GPL(kvm_read_guest_page); > > > > @@ -2277,7 +2321,8 @@ int kvm_vcpu_read_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, void *data, > > { > > struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn); > > > > - return __kvm_read_guest_page(slot, gfn, data, offset, len); > > + return __kvm_read_guest_page(slot, gfn, data, offset, len, > > + vcpu->kvm->mem_protected); > > Personally, I would've just added 'struct kvm' pointer to 'struct > kvm_memory_slot' to be able to extract 'mem_protected' info when > needed. This will make the patch much smaller. Okay, can do. Other thing I tried is to have per-slot flag to indicate that it's protected. But Sean pointed that it's all-or-nothing feature and having the flag in the slot would be misleading. > > } > > EXPORT_SYMBOL_GPL(kvm_vcpu_read_guest_page); > > > > @@ -2350,7 +2395,8 @@ int kvm_vcpu_read_guest_atomic(struct kvm_vcpu *vcpu, gpa_t gpa, > > EXPORT_SYMBOL_GPL(kvm_vcpu_read_guest_atomic); > > > > static int __kvm_write_guest_page(struct kvm_memory_slot *memslot, gfn_t gfn, > > - const void *data, int offset, int len) > > + const void *data, int offset, int len, > > + bool protected) > > { > > int r; > > unsigned long addr; > > @@ -2358,7 +2404,11 @@ static int __kvm_write_guest_page(struct kvm_memory_slot *memslot, gfn_t gfn, > > addr = gfn_to_hva_memslot(memslot, gfn); > > if (kvm_is_error_hva(addr)) > > return -EFAULT; > > - r = __copy_to_user((void __user *)addr + offset, data, len); > > + > > + if (protected) > > + r = copy_to_guest(addr + offset, data, len); > > + else > > + r = __copy_to_user((void __user *)addr + offset, data, len); > > All users of copy_to_guest() will have to have the same 'if (protected)' > check, right? Why not move the check to copy_to/from_guest() then? Good point. > > if (r) > > return -EFAULT; > > mark_page_dirty_in_slot(memslot, gfn); > > @@ -2370,7 +2420,8 @@ int kvm_write_guest_page(struct kvm *kvm, gfn_t gfn, > > { > > struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn); > > > > - return __kvm_write_guest_page(slot, gfn, data, offset, len); > > + return __kvm_write_guest_page(slot, gfn, data, offset, len, > > + kvm->mem_protected); > > } > > EXPORT_SYMBOL_GPL(kvm_write_guest_page); > > > > @@ -2379,7 +2430,8 @@ int kvm_vcpu_write_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, > > { > > struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn); > > > > - return __kvm_write_guest_page(slot, gfn, data, offset, len); > > + return __kvm_write_guest_page(slot, gfn, data, offset, len, > > + vcpu->kvm->mem_protected); > > } > > EXPORT_SYMBOL_GPL(kvm_vcpu_write_guest_page); > > > > @@ -2495,7 +2547,10 @@ int kvm_write_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc, > > if (unlikely(!ghc->memslot)) > > return kvm_write_guest(kvm, gpa, data, len); > > > > - r = __copy_to_user((void __user *)ghc->hva + offset, data, len); > > + if (kvm->mem_protected) > > + r = copy_to_guest(ghc->hva + offset, data, len); > > + else > > + r = __copy_to_user((void __user *)ghc->hva + offset, data, len); > > if (r) > > return -EFAULT; > > mark_page_dirty_in_slot(ghc->memslot, gpa >> PAGE_SHIFT); > > @@ -2530,7 +2585,10 @@ int kvm_read_guest_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc, > > if (unlikely(!ghc->memslot)) > > return kvm_read_guest(kvm, ghc->gpa, data, len); > > > > - r = __copy_from_user(data, (void __user *)ghc->hva, len); > > + if (kvm->mem_protected) > > + r = copy_from_guest(data, ghc->hva, len); > > + else > > + r = __copy_from_user(data, (void __user *)ghc->hva, len); > > if (r) > > return -EFAULT; > > -- > Vitaly > > -- Kirill A. Shutemov