Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Tue, 14 May 2019 19:05:22 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Alexandre Chartre <alexandre.chartre@oracle.com>
Cc:     Andy Lutomirski <luto@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim Krcmar <rkrcmar@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        kvm list <kvm@vger.kernel.org>, X86 ML <x86@kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        jan.setjeeilers@oracle.com, Liran Alon <liran.alon@oracle.com>,
        Jonathan Adams <jwadams@google.com>
Subject: Re: [RFC KVM 18/27] kvm/isolation: function to copy page table
 entries for percpu buffer
Message-ID: <20190514170522.GW2623@hirez.programming.kicks-ass.net>
References: <1557758315-12667-1-git-send-email-alexandre.chartre@oracle.com>
 <1557758315-12667-19-git-send-email-alexandre.chartre@oracle.com>
 <CALCETrWUKZv=wdcnYjLrHDakamMBrJv48wp2XBxZsEmzuearRQ@mail.gmail.com>
 <20190514070941.GE2589@hirez.programming.kicks-ass.net>
 <b8487de1-83a8-2761-f4a6-26c583eba083@oracle.com>
 <B447B6E8-8CEF-46FF-9967-DFB2E00E55DB@amacapital.net>
 <4e7d52d7-d4d2-3008-b967-c40676ed15d2@oracle.com>
 <CALCETrXtwksWniEjiWKgZWZAyYLDipuq+sQ449OvDKehJ3D-fg@mail.gmail.com>
 <e5fedad9-4607-0aa4-297e-398c0e34ae2b@oracle.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <e5fedad9-4607-0aa4-297e-398c0e34ae2b@oracle.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Tue, May 14, 2019 at 06:24:48PM +0200, Alexandre Chartre wrote:
> On 5/14/19 5:23 PM, Andy Lutomirski wrote:

> > How important is the ability to enable IRQs while running with the KVM
> > page tables?
> > 
> 
> I can't say, I would need to check but we probably need IRQs at least for
> some timers. Sounds like you would really prefer IRQs to be disabled.
> 

I think what amluto is getting at, is:

again:
	local_irq_disable();
	switch_to_kvm_mm();
	/* do very little -- (A) */
	VMEnter()

		/* runs as guest */

	/* IRQ happens */
	WMExit()
	/* inspect exit raisin */
	if (/* IRQ pending */) {
		switch_from_kvm_mm();
		local_irq_restore();
		goto again;
	}


but I don't know anything about VMX/SVM at all, so the above might not
be feasible, specifically I read something about how VMX allows NMIs
where SVM did not somewhere around (A) -- or something like that,
earlier in this thread.