From: Sean Christopherson <seanjc@google.com>
To: Kai Huang <kai.huang@intel.com>
Cc: "binbin.wu@linux.intel.com" <binbin.wu@linux.intel.com>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"pbonzini@redhat.com" <pbonzini@redhat.com>,
"robert.hu@linux.intel.com" <robert.hu@linux.intel.com>,
Chao Gao <chao.gao@intel.com>
Subject: Re: [PATCH v6 2/7] KVM: VMX: Use is_64_bit_mode() to check 64-bit mode
Date: Mon, 3 Apr 2023 08:02:52 -0700 [thread overview]
Message-ID: <ZCrqZTZWd1LC5s3J@google.com> (raw)
In-Reply-To: <fc92490afc7ee1b9679877878de64ad129853cc0.camel@intel.com>
On Mon, Apr 03, 2023, Huang, Kai wrote:
> >
> > I checked the code again and find the comment of
> > nested_vmx_check_permission().
> >
> > "/*
> > �* Intel's VMX Instruction Reference specifies a common set of
> > prerequisites
> > �* for running VMX instructions (except VMXON, whose prerequisites are
> > �* slightly different). It also specifies what exception to inject
> > otherwise.
> > �* Note that many of these exceptions have priority over VM exits, so they
> > �* don't have to be checked again here.
> > �*/"
> >
> > I think the Note part in the comment has tried to callout why the check
> > for compatibility mode is unnecessary.
> >
> > But I have a question here, nested_vmx_check_permission() checks that the
> > vcpu is vmxon, otherwise it will inject a #UD. Why this #UD is handled in
> > the VMExit handler specifically? Not all #UDs have higher priority than VM
> > exits?
> >
> > According to SDM Section "Relative Priority of Faults and VM Exits":
> > "Certain exceptions have priority over VM exits. These include
> > invalid-opcode exceptions, ..."
> > Seems not further classifications of #UDs.
>
> This is clarified in the pseudo code of VMX instructions in the SDM. If you
> look at the pseudo code, all VMX instructions except VMXON (obviously) have
> something like below:
>
> IF (not in VMX operation) ...
> THEN #UD;
> ELSIF in VMX non-root operation
> THEN VMexit;
>
> So to me "this particular" #UD has higher priority over VM exits (while other
> #UDs may not).
> But IIUC above #UD won't happen when running VMX instruction in the guest,
> because if there's any live guest, the CPU must already have been in VMX
> operation. So below check in nested_vmx_check_permission():
>
> if (!to_vmx(vcpu)->nested.vmxon) {
> kvm_queue_exception(vcpu, UD_VECTOR);
> return 0;
> }
>
> is needed to emulate the case that guest runs any other VMX instructions before
> VMXON.
Yep. IMO, the pseucode is misleading/confusing, the "in VMX non-root operation"
check should really come first. The VMXON pseudocode has the same awkward
sequence:
IF (register operand) or (CR0.PE = 0) or (CR4.VMXE = 0) or ...
THEN #UD;
ELSIF not in VMX operation
THEN
IF (CPL > 0) or (in A20M mode) or
(the values of CR0 and CR4 are not supported in VMX operation)
THEN #GP(0);
ELSIF in VMX non-root operation
THEN VMexit;
ELSIF CPL > 0
THEN #GP(0);
ELSE VMfail("VMXON executed in VMX root operation");
FI;
whereas I find this sequence for VMXON more representative of what actually happens:
IF (register operand) or (CR0.PE = 0) or (CR4.VMXE = 0) or ...
THEN #UD
IF in VMX non-root operation
THEN VMexit;
IF CPL > 0
THEN #GP(0)
IF in VMX operation
THEN VMfail("VMXON executed in VMX root operation");
IF (in A20M mode) or
(the values of CR0 and CR4 are not supported in VMX operation)
THEN #GP(0);
> > Anyway, I will seperate this patch from the LAM KVM enabling patch. And
> > send a patch seperately if needed later.
>
> I think your change for SGX is still needed based on the pseudo code of ENCLS.
Agreed.
next prev parent reply other threads:[~2023-04-03 15:02 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-19 8:49 [PATCH v6 0/7] Linear Address Masking (LAM) KVM Enabling Binbin Wu
2023-03-19 8:49 ` [PATCH v6 1/7] KVM: x86: Explicitly cast ulong to bool in kvm_set_cr3() Binbin Wu
2023-03-20 1:30 ` Binbin Wu
2023-03-19 8:49 ` [PATCH v6 2/7] KVM: VMX: Use is_64_bit_mode() to check 64-bit mode Binbin Wu
2023-03-20 12:36 ` Chao Gao
2023-03-20 12:51 ` Binbin Wu
2023-03-21 21:35 ` Sean Christopherson
2023-03-22 1:09 ` Binbin Wu
2023-03-28 23:33 ` Huang, Kai
2023-03-29 1:27 ` Binbin Wu
2023-03-29 2:04 ` Huang, Kai
2023-03-29 2:08 ` Binbin Wu
2023-03-29 17:34 ` Sean Christopherson
2023-03-29 22:46 ` Huang, Kai
2023-04-03 3:37 ` Binbin Wu
2023-04-03 11:24 ` Huang, Kai
2023-04-03 15:02 ` Sean Christopherson [this message]
2023-04-03 23:13 ` Huang, Kai
2023-04-04 1:21 ` Binbin Wu
2023-04-04 1:53 ` Huang, Kai
2023-04-04 2:45 ` Binbin Wu
2023-04-04 3:09 ` Huang, Kai
2023-04-04 3:15 ` Binbin Wu
2023-04-04 3:27 ` Binbin Wu
2023-04-04 1:31 ` Binbin Wu
2023-04-04 6:14 ` Binbin Wu
2023-03-20 22:36 ` Huang, Kai
2023-03-19 8:49 ` [PATCH v6 3/7] KVM: x86: Virtualize CR4.LAM_SUP Binbin Wu
2023-03-19 8:49 ` [PATCH v6 4/7] KVM: x86: Virtualize CR3.LAM_{U48,U57} Binbin Wu
2023-03-30 8:33 ` Yang, Weijiang
2023-03-30 8:40 ` Binbin Wu
2023-03-19 8:49 ` [PATCH v6 5/7] KVM: x86: Introduce untag_addr() in kvm_x86_ops Binbin Wu
2023-03-20 12:07 ` Chao Gao
2023-03-20 12:23 ` Binbin Wu
2023-03-29 1:54 ` Binbin Wu
2023-03-19 8:49 ` [PATCH v6 6/7] KVM: x86: Untag address when LAM applicable Binbin Wu
2023-03-20 11:51 ` Chao Gao
2023-03-20 11:56 ` Binbin Wu
2023-03-20 12:04 ` Binbin Wu
2023-03-29 5:02 ` Binbin Wu
2023-03-19 8:49 ` [PATCH v6 7/7] KVM: x86: Expose LAM feature to userspace VMM Binbin Wu
2023-03-20 8:57 ` Chao Gao
2023-03-20 12:00 ` Binbin Wu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=ZCrqZTZWd1LC5s3J@google.com \
--to=seanjc@google.com \
--cc=binbin.wu@linux.intel.com \
--cc=chao.gao@intel.com \
--cc=kai.huang@intel.com \
--cc=kvm@vger.kernel.org \
--cc=pbonzini@redhat.com \
--cc=robert.hu@linux.intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).