linux-kernel - Re: [PATCH] KVM: SVM: fix task switch emulation on INTn instruction.

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Message-ID: <034401953bc935d997c143153938edb1034b52cd.camel@redhat.com>
Date:   Thu, 14 Jul 2022 16:57:56 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Jim Mattson <jmattson@...gle.com>,
        kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: SVM: fix task switch emulation on INTn instruction.

On Thu, 2022-07-14 at 15:50 +0200, Maciej S. Szmigiero wrote:
> On 14.07.2022 14:44, Maxim Levitsky wrote:
> > Recently KVM's SVM code switched to re-injecting software interrupt events,
> > if something prevented their delivery.
> > 
> > Task switch due to task gate in the IDT, however is an exception
> > to this rule, because in this case, INTn instruction causes
> > a task switch intercept and its emulation completes the INTn
> > emulation as well.
> > 
> > Add a missing case to task_switch_interception for that.
> > 
> > This fixes 32 bit kvm unit test taskswitch2.
> > 
> > Fixes: 7e5b5ef8dca322 ("KVM: SVM: Re-inject INTn instead of retrying the insn on "failure"")
> > 
> > Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
> > ---
> 
> That's a good catch, your patch looks totally sensible to me.
> People running Win 3.x or OS/2 on top of KVM will surely be grateful for it :)

Yes and also people who run 32 bit kvm unit tests :)

BTW, I do have a win98 VM which I run once in a while under KVM.
On Intel it works very well, on AMD, only works without NPT and without MMU
pre-fetching, due to fact that the OS doesn't correctly invalidate TLB entries.

I do need to test KVM with OS/2 on one of the weekends.... ;-)

Thanks for the review,
	Best regards,
		Maxim Levitsky

> 
> Reviewed-by: Maciej S. Szmigiero <maciej.szmigiero@...cle.com>
> 
> Thanks,
> Maciej
>