From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Yang Weijiang <weijiang.yang@intel.com>
Cc: 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 10:58:08 -0800 [thread overview]
Message-ID: <20200114185808.GI16784@linux.intel.com> (raw)
In-Reply-To: <20200114030820.GA4583@local-michael-cet-test.sh.intel.com>
On Tue, Jan 14, 2020 at 11:08:20AM +0800, Yang Weijiang wrote:
> 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
I'm confused. It sounds like KVM_EXIT_SPP provides the instruction length
because it skips an instruction before exiting to userspace. But if KVM
is is emulating an instruction, it shouldn't be doing
{kvm_}skip_emulated_instruction(), e.g. if emulation fails due to a SPP
violation (returns KVM_EXIT_SPP) then GUEST_RIP should still point at the
exiting instruction. Ditto for the fast_page_fault() case, RIP shouldn't
be advanced.
What am I missing?
> 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?
I'm not convinced the instruction length needs to be provided to userspace
for this case. Obviously it's not difficult to provide the info, I just
don't understand the value added by doing so. As above, RIP shouldn't
need to be unwound, and blindly skipping an instruction seems like an odd
thing for a VMI engine to do.
> > 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.
Can we make SPP dependent on unrestricted guest so that the only entry
point to the emulator is through handle_ept_violation()? And thus the
only path to triggering KVM_EXIT_SPP would also be through
handle_ept_violation(); (I think, might be forgetting a different emulation
path).
>
> > 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 other threads:[~2020-01-14 18:58 UTC|newest]
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
2020-01-14 18:58 ` Sean Christopherson [this message]
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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