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[146.148.24.157]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e7e645d1fcsm15966584f8f.48.2025.09.16.04.58.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 16 Sep 2025 04:58:03 -0700 (PDT) Date: Tue, 16 Sep 2025 11:58:00 +0000 From: Mostafa Saleh To: Pranjal Shrivastava Cc: Will Deacon , linux-kernel@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev, maz@kernel.org, oliver.upton@linux.dev, joey.gouly@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, robin.murphy@arm.com, jean-philippe@linaro.org, qperret@google.com, tabba@google.com, jgg@ziepe.ca, mark.rutland@arm.com Subject: Re: [PATCH v4 01/28] KVM: arm64: Add a new function to donate memory with prot Message-ID: References: <20250819215156.2494305-1-smostafa@google.com> <20250819215156.2494305-2-smostafa@google.com> Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Sun, Sep 14, 2025 at 07:23:12PM +0000, Pranjal Shrivastava wrote: > On Tue, Sep 09, 2025 at 02:46:42PM +0100, Will Deacon wrote: > > On Tue, Aug 19, 2025 at 09:51:29PM +0000, Mostafa Saleh wrote: > > > Soon, IOMMU drivers running in the hypervisor might interact with > > > non-coherent devices, so it needs a mechanism to map memory as > > > non cacheable. > > > Add ___pkvm_host_donate_hyp() which accepts a new argument for prot, > > > so the driver can add KVM_PGTABLE_PROT_NORMAL_NC. > > > > > > Signed-off-by: Mostafa Saleh > > > --- > > > arch/arm64/kvm/hyp/include/nvhe/mem_protect.h | 1 + > > > arch/arm64/kvm/hyp/nvhe/mem_protect.c | 11 +++++++++-- > > > 2 files changed, 10 insertions(+), 2 deletions(-) > > > > > > diff --git a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > > > index 5f9d56754e39..52d7ee91e18c 100644 > > > --- a/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > > > +++ b/arch/arm64/kvm/hyp/include/nvhe/mem_protect.h > > > @@ -36,6 +36,7 @@ int __pkvm_prot_finalize(void); > > > int __pkvm_host_share_hyp(u64 pfn); > > > int __pkvm_host_unshare_hyp(u64 pfn); > > > int __pkvm_host_donate_hyp(u64 pfn, u64 nr_pages); > > > +int ___pkvm_host_donate_hyp(u64 pfn, u64 nr_pages, enum kvm_pgtable_prot prot); > > > int __pkvm_hyp_donate_host(u64 pfn, u64 nr_pages); > > > int __pkvm_host_share_ffa(u64 pfn, u64 nr_pages); > > > int __pkvm_host_unshare_ffa(u64 pfn, u64 nr_pages); > > > diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > > > index 8957734d6183..861e448183fd 100644 > > > --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c > > > +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > > > @@ -769,13 +769,15 @@ int __pkvm_host_unshare_hyp(u64 pfn) > > > return ret; > > > } > > > > > > -int __pkvm_host_donate_hyp(u64 pfn, u64 nr_pages) > > > +int ___pkvm_host_donate_hyp(u64 pfn, u64 nr_pages, enum kvm_pgtable_prot prot) > > > { > > > u64 phys = hyp_pfn_to_phys(pfn); > > > u64 size = PAGE_SIZE * nr_pages; > > > void *virt = __hyp_va(phys); > > > int ret; > > > > > > + WARN_ON(prot & KVM_PGTABLE_PROT_X); > > > > Should this actually just enforce that the permissions are > > KVM_PGTABLE_PROT_RW: > > > > WARN_ON((prot & KVM_PGTABLE_PROT_RWX) != KVM_PGTABLE_PROT_RW); > > > > ? > > > > Since the motivation is about the memory type rather than the > > permissions, it would be best to preserve the current behaviour. > > +1. I believe the current `WARN_ON(prot & KVM_PGTABLE_PROT_X);` check > would potentially allow "Read-only" or "Write-only" donations to slide > through silently. True, this can only be done from the hypervisor code though, I will make the check stricter as Will suggested, and if needed we can relax that later. Thanks, Mostafa > > > > > Will > > Thanks, > Praan