linux-kernel - Re: [RFC KVM 18/27] kvm/isolation: function to copy page table entries for percpu buffer

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Message-ID: <20190514170522.GW2623@hirez.programming.kicks-ass.net>
Date:   Tue, 14 May 2019 19:05:22 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexandre Chartre <alexandre.chartre@...cle.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        kvm list <kvm@...r.kernel.org>, X86 ML <x86@...nel.org>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        jan.setjeeilers@...cle.com, Liran Alon <liran.alon@...cle.com>,
        Jonathan Adams <jwadams@...gle.com>
Subject: Re: [RFC KVM 18/27] kvm/isolation: function to copy page table
 entries for percpu buffer

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.