RE: [RFC PATCH v4 6/7] KVM: x86: Add a new guest_debug flag forcing exit to userspace

[Kechen Lu]

> -----Original Message-----
> From: Sean Christopherson <seanjc@xxxxxxxxxx>
> Sent: Wednesday, July 20, 2022 10:06 AM
> To: Kechen Lu <kechenl@xxxxxxxxxx>
> Cc: kvm@xxxxxxxxxxxxxxx; pbonzini@xxxxxxxxxx; chao.gao@xxxxxxxxx;
> vkuznets@xxxxxxxxxx; Somdutta Roy <somduttar@xxxxxxxxxx>; linux-
> kernel@xxxxxxxxxxxxxxx
> Subject: Re: [RFC PATCH v4 6/7] KVM: x86: Add a new guest_debug flag
> forcing exit to userspace
> 
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> 
> On Tue, Jun 21, 2022, Kechen Lu wrote:
> > For debug and test purposes, there are needs to explicitly make
> > instruction triggered exits could be trapped to userspace. Simply add
> > a new flag for guest_debug interface could achieve this.
> >
> > This patch also fills the userspace accessible field
> > vcpu->run->hw.hardware_exit_reason for userspace to determine the
> > original triggered VM-exits.
> 
> This patch belongs in a different series, AFAICT there are no dependencies
> between this and allowing per-vCPU disabling of exits.  Allowing userspace to
> exit on "every" instruction exit is going to be much more controversial,
> largely because it will be difficult for KVM to provide a consistent, robust ABI.
> E.g. should KVM exit to userspace if an intercepted instruction is
> encountered by the emualtor?
> 
> TL;DR: drop this patch from the next version.

Ack. This patch I introduced as prerequisite for the patch 7 of implementing the selftests for KVM_CAP_X86_DISABLE_EXITS. But yeah, it's not a good practice, I will try to think about a better way to implement the disabled exits testing.

BR,
Kechen