linux-kernel - Re: [PATCH v7 041/102] KVM: VMX: Introduce test mode related to EPT violation VE

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Message-ID: <af9e3b06ba9e16df4bfd768dfdd78f2e0277cbe5.camel@intel.com>
Date:   Thu, 28 Jul 2022 12:54:20 +1200
From:   Kai Huang <kai.huang@...el.com>
To:     Isaku Yamahata <isaku.yamahata@...il.com>
Cc:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v7 041/102] KVM: VMX: Introduce test mode related to EPT
 violation VE

On Wed, 2022-07-27 at 16:39 -0700, Isaku Yamahata wrote:
> On Wed, Jul 20, 2022 at 05:13:08PM +1200,
> Kai Huang <kai.huang@...el.com> wrote:
> 
> > On Tue, 2022-07-19 at 07:49 -0700, Isaku Yamahata wrote:
> > > On Fri, Jul 08, 2022 at 02:23:43PM +1200,
> > > Kai Huang <kai.huang@...el.com> wrote:
> > > 
> > > > On Mon, 2022-06-27 at 14:53 -0700, isaku.yamahata@...el.com wrote:
> > > > > From: Isaku Yamahata <isaku.yamahata@...el.com>
> > > > > 
> > > > > To support TDX, KVM is enhanced to operate with #VE.  For TDX, KVM programs
> > > > > to inject #VE conditionally and set #VE suppress bit in EPT entry.  For VMX
> > > > > case, #VE isn't used.  If #VE happens for VMX, it's a bug.  To be
> > > > > defensive (test that VMX case isn't broken), introduce option
> > > > > ept_violation_ve_test and when it's set, set error.
> > > > 
> > > > I don't see why we need this patch.  It may be helpful during your test, but why
> > > > do we need this patch for formal submission?
> > > > 
> > > > And for a normal guest, what prevents one vcpu from sending #VE IPI to another
> > > > vcpu?
> > > 
> > > Paolo suggested it as follows.  Maybe it should be kernel config.
> > > (I forgot to add suggested-by. I'll add it)
> > > 
> > > https://lore.kernel.org/lkml/84d56339-4a8a-6ddb-17cb-12074588ba9c@redhat.com/
> > > 
> > > > 
> > 
> > OK.  But can we assume a normal guest won't sending #VE IPI?
> 
> Theoretically nothing prevents that.  I wouldn't way "normal".
> Anyway this is off by default.

I don't think whether it is on or off by default matters.  If it can happen
legitimately in the guest, it doesn't look right to print out something like
below:

	pr_err("VMEXIT due to unexpected #VE.\n");

Anyway, will let maintainers to decide.

-- 
Thanks,
-Kai