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[134.134.136.20]) by mx.google.com with ESMTPS id u9si17016571pls.145.2019.05.13.08.50.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 13 May 2019 08:50:22 -0700 (PDT) Received-SPF: pass (google.com: domain of dave.hansen@intel.com designates 134.134.136.20 as permitted sender) client-ip=134.134.136.20; Authentication-Results: mx.google.com; spf=pass (google.com: domain of dave.hansen@intel.com designates 134.134.136.20 as permitted sender) smtp.mailfrom=dave.hansen@intel.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=intel.com X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga003.jf.intel.com ([10.7.209.27]) by orsmga101.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 13 May 2019 08:50:22 -0700 X-ExtLoop1: 1 Received: from nsmith1-mobl.amr.corp.intel.com (HELO [10.251.15.98]) ([10.251.15.98]) by orsmga003.jf.intel.com with ESMTP; 13 May 2019 08:50:20 -0700 Subject: Re: [RFC KVM 19/27] kvm/isolation: initialize the KVM page table with core mappings To: Alexandre Chartre , pbonzini@redhat.com, rkrcmar@redhat.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, kvm@vger.kernel.org, x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: konrad.wilk@oracle.com, jan.setjeeilers@oracle.com, liran.alon@oracle.com, jwadams@google.com References: <1557758315-12667-1-git-send-email-alexandre.chartre@oracle.com> <1557758315-12667-20-git-send-email-alexandre.chartre@oracle.com> From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <1557758315-12667-20-git-send-email-alexandre.chartre@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: > + /* > + * Copy the mapping for all the kernel text. We copy at the PMD > + * level since the PUD is shared with the module mapping space. > + */ > + rv = kvm_copy_mapping((void *)__START_KERNEL_map, KERNEL_IMAGE_SIZE, > + PGT_LEVEL_PMD); > + if (rv) > + goto out_uninit_page_table; Could you double-check this? We (I) have had some repeated confusion with the PTI code and kernel text vs. kernel data vs. __init. KERNEL_IMAGE_SIZE looks to be 512MB which is quite a bit bigger than kernel text. > + /* > + * Copy the mapping for cpu_entry_area and %esp fixup stacks > + * (this is based on the PTI userland address space, but probably > + * not needed because the KVM address space is not directly > + * enterered from userspace). They can both be copied at the P4D > + * level since they each have a dedicated P4D entry. > + */ > + rv = kvm_copy_mapping((void *)CPU_ENTRY_AREA_PER_CPU, P4D_SIZE, > + PGT_LEVEL_P4D); > + if (rv) > + goto out_uninit_page_table; cpu_entry_area is used for more than just entry from userspace. The gdt mapping, for instance, is needed everywhere. You might want to go look at 'struct cpu_entry_area' in some more detail. > +#ifdef CONFIG_X86_ESPFIX64 > + rv = kvm_copy_mapping((void *)ESPFIX_BASE_ADDR, P4D_SIZE, > + PGT_LEVEL_P4D); > + if (rv) > + goto out_uninit_page_table; > +#endif Why are these mappings *needed*? I thought we only actually used these fixup stacks for some crazy iret-to-userspace handling. We're certainly not doing that from KVM context. Am I forgetting something? > +#ifdef CONFIG_VMAP_STACK > + /* > + * Interrupt stacks are vmap'ed with guard pages, so we need to > + * copy mappings. > + */ > + for_each_possible_cpu(cpu) { > + stack = per_cpu(hardirq_stack_ptr, cpu); > + pr_debug("IRQ Stack %px\n", stack); > + if (!stack) > + continue; > + rv = kvm_copy_ptes(stack - IRQ_STACK_SIZE, IRQ_STACK_SIZE); > + if (rv) > + goto out_uninit_page_table; > + } > + > +#endif I seem to remember that the KVM VMENTRY/VMEXIT context is very special. Interrupts (and even NMIs?) are disabled. Would it be feasible to do the switching in there so that we never even *get* interrupts in the KVM context? I also share Peter's concerns about letting modules do this. If we ever go down this road, we're going to have to think very carefully how we let KVM do this without giving all the not-so-nice out-of-tree modules the keys to the castle. A high-level comment: it looks like this is "working", but has probably erred on the side of mapping too much. The hard part is paring this back to a truly minimal set of mappings.