linux-kernel - Re: [PATCH 1/3] x86: KVM: VMX: Wrap GUEST_IA32_DEBUGCTL read/write with access functions

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Message-ID: <aCSof_0F2mE9gMYh@google.com>
Date: Wed, 14 May 2025 07:28:15 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: mlevitsk@...hat.com
Cc: kvm@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>, 
	Paolo Bonzini <pbonzini@...hat.com>, x86@...nel.org, 
	Dave Hansen <dave.hansen@...ux.intel.com>, Ingo Molnar <mingo@...hat.com>, 
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 1/3] x86: KVM: VMX: Wrap GUEST_IA32_DEBUGCTL read/write
 with access functions

On Mon, May 12, 2025, mlevitsk@...hat.com wrote:
> On Wed, 2025-05-07 at 10:18 -0700, Sean Christopherson wrote:
> AFAIK the KVM convention for msr writes is that 1 is GP, 0 success, and
> negative value exits as a KVM internal error to userspace. Not very developer
> friendly IMHO, there is a room for improvement here.

Yeah, it's ugly.  You're definitely not the first person to complain about KVM's
error code shenanigans.  Unfortunately, disentangling everything and doing so in
a way that is maintainable in the long term would be quite tricky, and absurdly
invasive. :-/