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Tue, 07 Mar 2023 16:13:26 -0800 (PST) Date: Wed, 08 Mar 2023 00:13:24 +0000 In-Reply-To: <20230128140030.GB700688@chaop.bj.intel.com> (message from Chao Peng on Sat, 28 Jan 2023 22:00:30 +0800) Mime-Version: 1.0 Message-ID: Subject: Re: [PATCH v10 9/9] KVM: Enable and expose KVM_MEM_PRIVATE From: Ackerley Tng To: Chao Peng Cc: seanjc@google.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-api@vger.kernel.org, linux-doc@vger.kernel.org, qemu-devel@nongnu.org, pbonzini@redhat.com, corbet@lwn.net, vkuznets@redhat.com, wanpengli@tencent.com, jmattson@google.com, joro@8bytes.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, arnd@arndb.de, naoya.horiguchi@nec.com, linmiaohe@huawei.com, x86@kernel.org, hpa@zytor.com, hughd@google.com, jlayton@kernel.org, bfields@fieldses.org, akpm@linux-foundation.org, shuah@kernel.org, rppt@kernel.org, steven.price@arm.com, mail@maciej.szmigiero.name, vbabka@suse.cz, vannapurve@google.com, yu.c.zhang@linux.intel.com, kirill.shutemov@linux.intel.com, luto@kernel.org, jun.nakajima@intel.com, dave.hansen@intel.com, ak@linux.intel.com, david@redhat.com, aarcange@redhat.com, ddutile@redhat.com, dhildenb@redhat.com, qperret@google.com, tabba@google.com, michael.roth@amd.com, mhocko@suse.com, wei.w.wang@intel.com Content-Type: text/plain; charset="UTF-8"; format=flowed; delsp=yes Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Chao Peng writes: > On Sat, Jan 14, 2023 at 12:01:01AM +0000, Sean Christopherson wrote: >> On Fri, Dec 02, 2022, Chao Peng wrote: > ... >> Strongly prefer to use similar logic to existing code that detects wraps: >> mem->restricted_offset + mem->memory_size < mem->restricted_offset >> This is also where I'd like to add the "gfn is aligned to offset" check, >> though >> my brain is too fried to figure that out right now. > Used count_trailing_zeros() for this TODO, unsure we have other better > approach. > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index afc8c26fa652..fd34c5f7cd2f 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -56,6 +56,7 @@ > #include > #include > #include > +#include > #include "coalesced_mmio.h" > #include "async_pf.h" > @@ -2087,6 +2088,19 @@ static bool kvm_check_memslot_overlap(struct > kvm_memslots *slots, int id, > return false; > } > +/* > + * Return true when ALIGNMENT(offset) >= ALIGNMENT(gpa). > + */ > +static bool kvm_check_rmem_offset_alignment(u64 offset, u64 gpa) > +{ > + if (!offset) > + return true; > + if (!gpa) > + return false; > + > + return !!(count_trailing_zeros(offset) >= count_trailing_zeros(gpa)); Perhaps we could do something like #define lowest_set_bit(val) (val & -val) and use return lowest_set_bit(offset) >= lowest_set_bit(gpa); Please help me to understand: why must ALIGNMENT(offset) >= ALIGNMENT(gpa)? Why is it not sufficient to have both gpa and offset be aligned to PAGE_SIZE? > +} > + > /* > * Allocate some memory and give it an address in the guest physical > address > * space. > @@ -2128,7 +2142,8 @@ int __kvm_set_memory_region(struct kvm *kvm, > if (mem->flags & KVM_MEM_PRIVATE && > (mem->restrictedmem_offset & (PAGE_SIZE - 1) || > mem->restrictedmem_offset + mem->memory_size < > mem->restrictedmem_offset || > - 0 /* TODO: require gfn be aligned with restricted offset */)) > + !kvm_check_rmem_offset_alignment(mem->restrictedmem_offset, > + mem->guest_phys_addr))) > return -EINVAL; > if (as_id >= kvm_arch_nr_memslot_as_ids(kvm) || id >= KVM_MEM_SLOTS_NUM) > return -EINVAL;