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From: Oliver Upton To: Catalin Marinas Cc: ankita@nvidia.com, jgg@nvidia.com, maz@kernel.org, james.morse@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, reinette.chatre@intel.com, surenb@google.com, stefanha@redhat.com, brauner@kernel.org, will@kernel.org, mark.rutland@arm.com, alex.williamson@redhat.com, kevin.tian@intel.com, yi.l.liu@intel.com, ardb@kernel.org, akpm@linux-foundation.org, andreyknvl@gmail.com, wangjinchao@xfusion.com, gshan@redhat.com, ricarkol@google.com, linux-mm@kvack.org, lpieralisi@kernel.org, rananta@google.com, ryan.roberts@arm.com, aniketa@nvidia.com, cjia@nvidia.com, kwankhede@nvidia.com, targupta@nvidia.com, vsethi@nvidia.com, acurrid@nvidia.com, apopple@nvidia.com, jhubbard@nvidia.com, danw@nvidia.com, kvmarm@lists.linux.dev, mochs@nvidia.com, zhiw@nvidia.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v6 1/4] kvm: arm64: introduce new flag for non-cacheable IO memory Message-ID: References: <20240207204652.22954-1-ankita@nvidia.com> <20240207204652.22954-2-ankita@nvidia.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT On Thu, Feb 08, 2024 at 01:00:59PM +0000, Catalin Marinas wrote: > On Thu, Feb 08, 2024 at 02:16:49AM +0530, ankita@nvidia.com wrote: > > diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c > > index c651df904fe3..2a893724ee9b 100644 > > --- a/arch/arm64/kvm/hyp/pgtable.c > > +++ b/arch/arm64/kvm/hyp/pgtable.c > > @@ -717,15 +717,28 @@ void kvm_tlb_flush_vmid_range(struct kvm_s2_mmu *mmu, > > static int stage2_set_prot_attr(struct kvm_pgtable *pgt, enum kvm_pgtable_prot prot, > > kvm_pte_t *ptep) > > { > > - bool device = prot & KVM_PGTABLE_PROT_DEVICE; > > - kvm_pte_t attr = device ? KVM_S2_MEMATTR(pgt, DEVICE_nGnRE) : > > - KVM_S2_MEMATTR(pgt, NORMAL); > > + kvm_pte_t attr; > > u32 sh = KVM_PTE_LEAF_ATTR_LO_S2_SH_IS; > > > > + switch (prot & (KVM_PGTABLE_PROT_DEVICE | > > + KVM_PGTABLE_PROT_NORMAL_NC)) { > > + case 0: > > + attr = KVM_S2_MEMATTR(pgt, NORMAL); > > + break; > > + case KVM_PGTABLE_PROT_DEVICE: > > + if (prot & KVM_PGTABLE_PROT_X) > > + return -EINVAL; > > + attr = KVM_S2_MEMATTR(pgt, DEVICE_nGnRE); > > + break; > > + case KVM_PGTABLE_PROT_NORMAL_NC: > > + attr = KVM_S2_MEMATTR(pgt, NORMAL_NC); > > + break; > > Does it make sense to allow executable here as well? I don't think it's > harmful but not sure there's a use-case for it either. Ah, we should just return EINVAL for that too. I get that the memory attribute itself is not problematic, but since we're only using this thing for MMIO it'd be a rather massive bug in KVM... We reject attempts to do this earlier in user_mem_abort(). If, for some reason, we wanted to do Normal-NC actual memory then we would need to make sure that KVM does the appropriate cache maintenance at map / unmap. -- Thanks, Oliver