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From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>,
	Yang Weijiang <weijiang.yang@intel.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	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, 21 Jan 2020 15:14:37 +0100
Message-ID: <5d4118d9-c501-6c59-82cc-50e317be195c@redhat.com> (raw)
In-Reply-To: <20200114185808.GI16784@linux.intel.com>

On 14/01/20 19:58, Sean Christopherson wrote:
> 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.
> 

The reason to introduce the instruction length was so that userspace
could blindly use SPP to emulate ROM behavior.  Weijiang's earlier
patches in fact _only_ provided that behavior, and I asked him to change
it so that, by default, using SPP and not handling it will basically
cause an infinite loop of SPP violations.

One possibility to clean things up is to change "fault_handled" and
fast_page_fault's return value from bool to RET_PF* (false becomes
RET_PF_INVALID, true becomes RET_PF_RETRY).  direct_page_fault would
also have to do something like

	r = fast_page_fault(vcpu, gpa, level, error_code))
	if (r != RET_PF_INVALID)
		return r;

Then fast_page_fault can just return RET_PF_USERSPACE, and this ugly
case can go away.

+		if (vcpu->run->exit_reason == KVM_EXIT_SPP)
+			r = RET_PF_USERSPACE;
+

Thanks,

Paolo


  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
2020-01-14 18:58           ` Sean Christopherson
2020-01-15  1:36             ` Yang Weijiang
2020-01-21 14:14             ` Paolo Bonzini [this message]
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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