From mboxrd@z Thu Jan 1 00:00:00 1970 From: Suraj Jitindar Singh Date: Fri, 22 Mar 2019 04:23:20 +0000 Subject: Re: [PATCH 1/3] KVM: PPC: Implement kvmppc_copy_guest() to perform in place copy of guest memory Message-Id: <1553228600.21249.3.camel@gmail.com> List-Id: References: <20190319040435.10716-1-sjitindarsingh@gmail.com> In-Reply-To: <20190319040435.10716-1-sjitindarsingh@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: kvm-ppc@vger.kernel.org On Tue, 2019-03-19 at 17:53 +1100, Alexey Kardashevskiy wrote: > > On 19/03/2019 15:04, Suraj Jitindar Singh wrote: > > Implement the function kvmppc_copy_guest() to be used to perform a > > memory > > copy from one guest physical address to another of a variable > > length. > > > > This performs similar functionality as the kvm_read_guest() and > > kvm_write_guest() functions, except both addresses point to guest > > memory. > > This performs a copy in place using raw_copy_in_user() to avoid > > having to > > buffer the data. > > > > The guest memory can reside in different memslots and the copy > > length > > can span memslots. > > > > Signed-off-by: Suraj Jitindar Singh > > --- > > arch/powerpc/kvm/book3s_hv.c | 69 > > ++++++++++++++++++++++++++++++++++++++++++++ > > 1 file changed, 69 insertions(+) > > > > diff --git a/arch/powerpc/kvm/book3s_hv.c > > b/arch/powerpc/kvm/book3s_hv.c > > index ec38576dc685..7179ea783f4f 100644 > > --- a/arch/powerpc/kvm/book3s_hv.c > > +++ b/arch/powerpc/kvm/book3s_hv.c > > @@ -814,6 +814,75 @@ static int kvmppc_h_set_mode(struct kvm_vcpu > > *vcpu, unsigned long mflags, > > } > > } > > > > +static int __kvmppc_copy_guest_page(struct kvm_memory_slot > > *to_memslot, > > + gfn_t to_gfn, int to_offset, > > + struct kvm_memory_slot > > *from_memslot, > > + gfn_t from_gfn, int > > from_offset, int len) > > +{ > > + int r; > > + unsigned long to_addr, from_addr; > > + > > + to_addr = gfn_to_hva_memslot(to_memslot, to_gfn); > > + if (kvm_is_error_hva(to_addr)) > > + return -EFAULT; > > + from_addr = gfn_to_hva_memslot(from_memslot, from_gfn); > > + if (kvm_is_error_hva(from_addr)) > > + return -EFAULT; > > + r = raw_copy_in_user((void __user *)to_addr + to_offset, > > + (void __user *)from_addr + > > from_offset, len); > > + if (r) > > + return -EFAULT; > > + return 0; > > +} > > + > > +static int next_segment_many(unsigned long len, int offset1, int > > offset2) > > > What is the "_many" suffix about? It made sense in the context of virt/kvm/kvm_main.c, maybe less so now I moved it to PPC code. > > > > +{ > > + int size = min(PAGE_SIZE - offset1, PAGE_SIZE - offset2); > > Nitpicking :) Here it is min()... > > > + > > + if (len > size) > > + return size; > > + else > > + return len; > > ...but here it is if() when it could also be min() (or may be > min_t()). Very true > > > > +} > > + > > +static int kvmppc_copy_guest(struct kvm *kvm, gpa_t to, gpa_t > > from, > > + unsigned long len) > > > This does not compile (most comments are made just because I had to > reply anyway): > > /home/aik/p/kernel/arch/powerpc/kvm/book3s_hv.c:835:12: error: > ‘kvmppc_copy_guest’ defined but not used [-Werror=unused-function] > static int kvmppc_copy_guest(struct kvm *kvm, gpa_t to, gpa_t from, > ^~~~~~~~~~~~~~~~~ > > imho 1/3 and 2/3 should be one patch. > > A general comment is that the H_PAGE_INIT hcall description says "The > logical addresses ... must both point to the start of a 4 K system > memory page" so the loop will never have to execute more than once, > cannot span memslots => it could be lot simpler then, or I missed > something here (unlikely, after reading 3/3). Yeah I think I'll roll 1/3 and 2/3 into one and only handle 4K pages for now. > > > > +{ > > + struct kvm_memory_slot *to_memslot = NULL; > > + struct kvm_memory_slot *from_memslot = NULL; > > + gfn_t to_gfn = to >> PAGE_SHIFT; > > + gfn_t from_gfn = from >> PAGE_SHIFT; > > + int seg; > > + int to_offset = offset_in_page(to); > > + int from_offset = offset_in_page(from); > > + int ret; > > + > > + while ((seg = next_segment_many(len, to_offset, > > from_offset)) != 0) { > > + if (!to_memslot || (to_gfn >= (to_memslot- > > >base_gfn + > > + to_memslot- > > >npages))) > > + to_memslot = gfn_to_memslot(kvm, to_gfn); > > + if (!from_memslot || (from_gfn >= (from_memslot- > > >base_gfn + > > + from_memslot- > > >npages))) > > + from_memslot = gfn_to_memslot(kvm, > > from_gfn); > > + > > + ret = __kvmppc_copy_guest_page(to_memslot, to_gfn, > > to_offset, > > + from_memslot, > > from_gfn, > > + from_offset, seg); > > + if (ret < 0) > > + return ret; > > + mark_page_dirty(kvm, to_gfn); > > > Nit: if you made mark_page_dirty_in_slot() public (yeah it is in the > common code), you could save here one search through memslots. Yeah, given we store the most recent memslot and check it first, I think the overhead is negligible. You are correct though. > > > > + > > + to_offset = (to_offset + seg) & (PAGE_SIZE - 1); > > > s/(PAGE_SIZE - 1)/~PAGE_MASK/ ? Or even use again that > offset_in_page() > as you did above? > > > > + from_offset = (from_offset + seg) & (PAGE_SIZE - > > 1); > > + len -= seg; > > + if (!to_offset) > > + to_gfn += 1; > > + if (!from_offset) > > + from_gfn += 1; > > + } > > + return 0; > > +} > > + > > static int kvm_arch_vcpu_yield_to(struct kvm_vcpu *target) > > { > > struct kvmppc_vcore *vcore = target->arch.vcore; > > > >