linux-kernel - Re: [RFC KVM 25/27] kvm/isolation: implement actual KVM isolation enter/exit

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Date:   Mon, 13 May 2019 09:01:14 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Alexandre Chartre <alexandre.chartre@...cle.com>
Cc:     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>,
        Andrew Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        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 25/27] kvm/isolation: implement actual KVM isolation enter/exit

On Mon, May 13, 2019 at 7:40 AM Alexandre Chartre
<alexandre.chartre@...cle.com> wrote:
>
> From: Liran Alon <liran.alon@...cle.com>
>
> KVM isolation enter/exit is done by switching between the KVM address
> space and the kernel address space.
>
> Signed-off-by: Liran Alon <liran.alon@...cle.com>
> Signed-off-by: Alexandre Chartre <alexandre.chartre@...cle.com>
> ---
>  arch/x86/kvm/isolation.c |   30 ++++++++++++++++++++++++------
>  arch/x86/mm/tlb.c        |    1 +
>  include/linux/sched.h    |    1 +
>  3 files changed, 26 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/isolation.c b/arch/x86/kvm/isolation.c
> index db0a7ce..b0c789f 100644
> --- a/arch/x86/kvm/isolation.c
> +++ b/arch/x86/kvm/isolation.c
> @@ -1383,11 +1383,13 @@ static bool kvm_page_fault(struct pt_regs *regs, unsigned long error_code,
>         printk(KERN_DEFAULT "KVM isolation: page fault %ld at %pS on %lx (%pS) while switching mm\n"
>                "  cr3=%lx\n"
>                "  kvm_mm=%px pgd=%px\n"
> -              "  active_mm=%px pgd=%px\n",
> +              "  active_mm=%px pgd=%px\n"
> +              "  kvm_prev_mm=%px pgd=%px\n",
>                error_code, (void *)regs->ip, address, (void *)address,
>                cr3,
>                &kvm_mm, kvm_mm.pgd,
> -              active_mm, active_mm->pgd);
> +              active_mm, active_mm->pgd,
> +              current->kvm_prev_mm, current->kvm_prev_mm->pgd);
>         dump_stack();
>
>         return false;
> @@ -1649,11 +1651,27 @@ void kvm_may_access_sensitive_data(struct kvm_vcpu *vcpu)
>         kvm_isolation_exit();
>  }
>
> +static void kvm_switch_mm(struct mm_struct *mm)
> +{
> +       unsigned long flags;
> +
> +       /*
> +        * Disable interrupt before updating active_mm, otherwise if an
> +        * interrupt occurs during the switch then the interrupt handler
> +        * can be mislead about the mm effectively in use.
> +        */
> +       local_irq_save(flags);
> +       current->kvm_prev_mm = current->active_mm;

Peter's NAK aside, why on Earth is this in task_struct?  You cannot
possibly context switch while in isolation mode.

--Andy