From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id CBAF23B14D2; Tue, 11 Aug 2026 15:42:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786462956; cv=none; b=ar4EHHn9FDXPU4UU8nwUdT+icFTWI6PNXPkHMx0hjoUA8iDVjWnCoQi92BDXQSFLEl7FJGo+1d2DaDLBtqhEtK0TgYbUj28Q+Xx3aptMzxw6z/+dfrLxOfwSeFWisXfW2J/zlzdgJ6okVjS9owh1vSoXLNupf/gU15ycpT6zpOw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786462956; c=relaxed/simple; bh=N3qnRTjJztvg5epuOANhnoAI4KJvsaIW+sRapJAXN0U=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=AF5LNm4XTRUk9rx25Res+M+LD4YrYd39Hdfe2SaxTfBbifjuAfsqULyl8/k5bjtp9BKeO7j4A1LopWGBTf5bbt4d1xaDtsKqgwmUuGxyWBz9cz/LSMH2FsEUSkyVOOKHwnlRJsrPxAGxfI/yw/+RkqnLsOjcWIEcq810NnGXM5s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=am/mA1sK; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="am/mA1sK" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 26D1D1516; Tue, 11 Aug 2026 08:42:30 -0700 (PDT) Received: from arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 238EC3F632; Tue, 11 Aug 2026 08:42:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1786462954; bh=N3qnRTjJztvg5epuOANhnoAI4KJvsaIW+sRapJAXN0U=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=am/mA1sK5zKjfitH7cRbZ87H8alzpMUQI8+jwTsN4PE48jXctVfydgElUScpeO1vs IA80CRzE5RJn8gXG/Utun8MLlkKfIN7KX/969mbtdhU6KQffIXWp+B1Imv4mGyOkfF 8epE3AiaUl1z/9uja+Du7UQunHcap01bytZVtlU4= Date: Tue, 11 Aug 2026 16:42:28 +0100 From: Catalin Marinas To: Steven Price Cc: kvm@vger.kernel.org, kvmarm@lists.linux.dev, Marc Zyngier , Will Deacon , James Morse , Oliver Upton , Suzuki K Poulose , Zenghui Yu , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Joey Gouly , Alexandru Elisei , Christoffer Dall , Fuad Tabba , linux-coco@lists.linux.dev, Ganapatrao Kulkarni , Gavin Shan , Shanker Donthineni , Alper Gun , "Aneesh Kumar K . V" , Emi Kisanuki , Vishal Annapurve , WeiLin.Chang@arm.com, Lorenzo Pieralisi Subject: Re: [PATCH v16 29/45] KVM: arm64: CCA: Support runtime faulting of memory Message-ID: References: <20260803134403.80630-1-steven.price@arm.com> <20260803134403.80630-30-steven.price@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@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: <20260803134403.80630-30-steven.price@arm.com> On Mon, Aug 03, 2026 at 02:43:45PM +0100, Steven Price wrote: > At runtime if the realm guest accesses memory which hasn't yet been > mapped then KVM needs to either populate the region or fault the guest. > > For memory in the lower (protected) region of IPA a fresh page is > provided to the RMM which will zero the contents. For memory in the > upper (shared) region of IPA, the memory from the memslot is mapped > into the realm VM non secure. Is this still true with in-place guestmem conversion? > @@ -1693,7 +1709,14 @@ static int gmem_abort(const struct kvm_s2_fault_desc *s2fd) > kvm_fault_lock(kvm); > if (mmu_invalidate_retry(kvm, mmu_seq)) { > ret = -EAGAIN; > - goto out_unlock; > + goto out_release_page; > + } > + > + if (kvm_is_realm(kvm)) { > + prot &= ~KVM_PGTABLE_PROT_X; > + ret = realm_map_ipa(kvm, s2fd->fault_ipa, pfn, > + PAGE_SIZE, prot, memcache); > + goto out_release_page; > } [...] > +int realm_map_ipa(struct kvm *kvm, phys_addr_t ipa, > + kvm_pfn_t pfn, unsigned long map_size, > + enum kvm_pgtable_prot prot, > + struct kvm_mmu_memory_cache *memcache) > +{ > + struct realm *realm = &kvm->arch.realm; > + > + ipa = ALIGN_DOWN(ipa, map_size); > + if (!kvm_realm_is_private_address(realm, ipa)) { > + return realm_map_non_secure(kvm, ipa, pfn, map_size, prot, > + memcache); > + } > + > + /* It's impossible to map protected pages read-only. */ > + if (WARN_ON(!(prot & KVM_PGTABLE_PROT_W))) > + return -EFAULT; > + return realm_map_protected(kvm, ipa, pfn, map_size, memcache); > +} I was trying to understand (with the help of some LLMs) to understand whether we can end up on the do_gpf() path as a result of VMM actions. The above kvm_realm_is_private_address() only checks for the IPA but does not check against guestmem if the page is truly private. I probably miss something but the scenario would be something like: 1. VMM creates the gmem region with GUEST_MEMFD_FLAG_MMAP | GUEST_MEMFD_FLAG_INIT_SHARED, mmap()able and GUP-pinnable 2. VMM starts an O_DIRECT write() from that mapping; the block layer FOLL_PINs the shared folio 3. VMM runs a vCPU so the realm touches the protected-IPA alias of the same gfn. gmem_abort() delegates the pinned, still-shared page to the RMM 4. The in-flight I/O then reads the now-Realm page from the kernel linear map. That access takes a GPF at EL1, so do_gpf() -> die_kernel_fault() x86, IIUC, also checks kvm_gmem_is_private(). They also have kvm_arch_gmem_make_private() triggered on the kvm_gmem_get_pfn() path but I got lost in the call sites, not sure whether that's strictly needed if we check both private IPA and kvm_gmem_is_private(). -- Catalin