From: Yang Weijiang <weijiang.yang@intel.com> To: Sean Christopherson <sean.j.christopherson@intel.com> Cc: Yang Weijiang <weijiang.yang@intel.com>, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, pbonzini@redhat.com, jmattson@google.com, yu.c.zhang@linux.intel.com, alazar@bitdefender.com, edwin.zhai@intel.com Subject: Re: [RESEND PATCH v10 06/10] vmx: spp: Set up SPP paging table at vmentry/vmexit Date: Tue, 14 Jan 2020 11:08:20 +0800 Message-ID: <20200114030820.GA4583@local-michael-cet-test.sh.intel.com> (raw) In-Reply-To: <20200113173358.GC1175@linux.intel.com> On Mon, Jan 13, 2020 at 09:33:58AM -0800, Sean Christopherson wrote: > On Mon, Jan 13, 2020 at 04:10:50PM +0800, Yang Weijiang wrote: > > On Fri, Jan 10, 2020 at 10:04:59AM -0800, Sean Christopherson wrote: > > > On Thu, Jan 02, 2020 at 02:13:15PM +0800, Yang Weijiang wrote: > > > > @@ -3585,7 +3602,30 @@ static bool fast_page_fault(struct kvm_vcpu *vcpu, gva_t gva, int level, > > > > if ((error_code & PFERR_WRITE_MASK) && > > > > spte_can_locklessly_be_made_writable(spte)) > > > > { > > > > - new_spte |= PT_WRITABLE_MASK; > > > > + /* > > > > + * Record write protect fault caused by > > > > + * Sub-page Protection, let VMI decide > > > > + * the next step. > > > > + */ > > > > + if (spte & PT_SPP_MASK) { > > > > + int len = kvm_x86_ops->get_inst_len(vcpu); > > > > > > There's got to be a better way to handle SPP exits than adding a helper > > > to retrieve the instruction length. > > > > > The fault instruction was skipped by kvm_skip_emulated_instruction() > > before, but Paolo suggested leave the re-do or skip option to user-space > > to make it flexible for write protection or write tracking, so return > > length to user-space. > > Sorry, my comment was unclear. I have no objection to punting the fault > to userspace, it's the mechanics of how it's done that I dislike. > > Specifically, (a) using run->exit_reason to propagate the SPP exit up the > stack, e.g. instead of modifying affected call stacks to play nice with > any exit to userspace, (b) assuming ->get_insn_len() will always be > accurate, e.g. see the various caveats in skip_emulated_instruction() for > both VMX and SVM, and (c) duplicating the state capture code in every > location that can encounter a SPP fault. How about calling skip_emulated_instruction() in KVM before exit to userspace, but still return the skipped instruction length, if userspace would like to re-execute the instruction, it can unwind RIP or simply rely on KVM? > > What I'm hoping is that it's possible to modify the call stacks to > explicitly propagate an exit to userspace and/or SPP fault, and shove all > the state capture into a common location, e.g. handle_ept_violation(). > The problem is, the state capture code in fast_page_fault() and emulation case share different causes, the former is generic occurence of SPP induced EPT violation, the latter is atually a "faked" one while detecting emulation instruction is writing some SPP protected area, so I seperated them. > Side topic, assuming the userspace VMI is going to be instrospecting the > faulting instruction, won't it decode the instruction? I.e. calculate > the instruction length anyways?
next prev parent reply index Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-01-02 6:13 [RESEND PATCH v10 00/10] Enable Sub-Page Write Protection Support Yang Weijiang 2020-01-02 6:13 ` [RESEND PATCH v10 01/10] Documentation: Add EPT based Subpage Protection and related APIs Yang Weijiang 2020-01-02 6:13 ` [RESEND PATCH v10 02/10] vmx: spp: Add control flags for Sub-Page Protection(SPP) Yang Weijiang 2020-01-10 16:58 ` Sean Christopherson 2020-01-13 5:44 ` Yang Weijiang 2020-01-02 6:13 ` [RESEND PATCH v10 03/10] mmu: spp: Add SPP Table setup functions Yang Weijiang 2020-01-10 17:26 ` Sean Christopherson 2020-01-13 6:00 ` Yang Weijiang 2020-01-10 17:40 ` Sean Christopherson 2020-01-13 6:04 ` Yang Weijiang 2020-01-02 6:13 ` [RESEND PATCH v10 04/10] mmu: spp: Add functions to operate SPP access bitmap Yang Weijiang 2020-01-10 17:38 ` Sean Christopherson 2020-01-13 6:15 ` Yang Weijiang 2020-01-02 6:13 ` [RESEND PATCH v10 05/10] x86: spp: Introduce user-space SPP IOCTLs Yang Weijiang 2020-01-10 18:10 ` Sean Christopherson 2020-01-13 8:21 ` Yang Weijiang 2020-01-02 6:13 ` [RESEND PATCH v10 06/10] vmx: spp: Set up SPP paging table at vmentry/vmexit Yang Weijiang 2020-01-10 17:55 ` Sean Christopherson 2020-01-13 6:50 ` Yang Weijiang 2020-01-21 14:01 ` Paolo Bonzini 2020-01-10 18:04 ` Sean Christopherson 2020-01-13 8:10 ` Yang Weijiang 2020-01-13 17:33 ` Sean Christopherson 2020-01-13 18:55 ` Adalbert Lazăr 2020-01-13 21:47 ` Sean Christopherson 2020-01-14 3:08 ` Yang Weijiang [this message] 2020-01-14 18:58 ` Sean Christopherson 2020-01-15 1:36 ` Yang Weijiang 2020-01-21 14:14 ` Paolo Bonzini 2020-01-02 6:13 ` [RESEND PATCH v10 07/10] mmu: spp: Enable Lazy mode SPP protection Yang Weijiang 2020-01-02 6:13 ` [RESEND PATCH v10 08/10] mmu: spp: Handle SPP protected pages when VM memory changes Yang Weijiang 2020-01-02 6:13 ` [RESEND PATCH v10 09/10] x86: spp: Add SPP protection check in emulation Yang Weijiang 2020-01-02 6:13 ` [RESEND PATCH v10 10/10] kvm: selftests: selftest for Sub-Page protection Yang Weijiang -- strict thread matches above, loose matches on Subject: below -- 2020-01-02 5:18 [RESEND PATCH v10 00/10] Enable Sub-Page Write Protection Support Yang Weijiang 2020-01-02 5:19 ` [RESEND PATCH v10 06/10] vmx: spp: Set up SPP paging table at vmentry/vmexit Yang Weijiang
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