linux-kernel - Re: [PATCH v2 3/6] KVM: VMX: Handle vectoring error in check_emulate

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Message-ID: <2b75550c-0dc7-4bcc-ac60-9ad4402c17f8@gmail.com>
Date: Wed, 11 Dec 2024 23:12:29 +0000
From: Ivan Orlov <ivan.orlov0322@...il.com>
To: Sean Christopherson <seanjc@...gle.com>, Ivan Orlov <iorlov@...zon.com>
Cc: bp@...en8.de, dave.hansen@...ux.intel.com, mingo@...hat.com,
 pbonzini@...hat.com, shuah@...nel.org, tglx@...utronix.de, hpa@...or.com,
 kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org, x86@...nel.org, pdurrant@...zon.co.uk,
 dwmw@...zon.co.uk
Subject: Re: [PATCH v2 3/6] KVM: VMX: Handle vectoring error in
 check_emulate_instruction

On 12/11/24 18:15, Sean Christopherson wrote:
> Hmm, this should probably be "pf_mmio", not just "mmio".  E.g. if KVM is emulating
> large swaths of guest code because unrestricted guest is disabled, then can end up
> emulating an MMIO access for "normal" emulation.
> 
> Hmm, actually, what if we go with this?
> 
>    static inline bool kvm_can_emulate_event_vectoring(int emul_type)
>    {
> 	return !(emul_type & EMULTYPE_PF) ||
> 	       (emul_type & EMULTYPE_WRITE_PF_TO_SP);
>    }
> 

Hm, by the way, what is the desired behaviour if EMULTYPE_ALLOW_RETRY_PF 
is set? Is it correct that we return an internal error if it is set 
during vectoring? Or KVM may try to unprotect the page and re-execute?

If so, we may need something like

static inline bool kvm_can_emulate_event_vectoring(int emul_type)
{
	return !(emul_type & EMULTYPE_PF) ||
	       (emul_type & ~(EMULTYPE_PF));
}

So it returns true if EMULTYPE_PF is not set or if it's not the only set 
bit.

-- 
Kind regards,
Ivan Orlov