linux-kernel - Re: [PATCH 0/3] KVM: x86: Fix supported VM

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Message-ID: <7f3001de041334b5c196b5436680473786a21816.camel@intel.com>
Date: Fri, 26 Apr 2024 01:17:11 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "Li, Xiaoyao" <xiaoyao.li@...el.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] KVM: x86: Fix supported VM_TYPES caps

On Thu, 2024-04-25 at 07:30 -0700, Sean Christopherson wrote:
> On Thu, Apr 25, 2024, Xiaoyao Li wrote:
> > On 4/24/2024 12:53 AM, Sean Christopherson wrote:
> > > Fix a goof where KVM fails to re-initialize the set of supported VM types,
> > > resulting in KVM overreporting the set of supported types when a vendor
> > > module is reloaded with incompatible settings.  E.g. unload kvm-intel.ko,
> > > reload with ept=0, and KVM will incorrectly treat SW_PROTECTED_VM as
> > > supported.
> > 
> > Hah, this reminds me of the bug of msrs_to_save[] and etc.
> > 
> >    7a5ee6edb42e ("KVM: X86: Fix initialization of MSR lists")
> 
> Yeah, and we had the same bug with allow_smaller_maxphyaddr
> 
>   88213da23514 ("kvm: x86: disable the narrow guest module parameter on unload")
> 
> If the side effects of linking kvm.ko into kvm-{amd,intel}.ko weren't so painful
> for userspace, 
> 

Do we have any real side effects for _userspace_ here?

> I would more seriously consider pursuing that in advance of
> multi-KVM[*].  Because having KVM be fully self-contained has some *really* nice
> properties, e.g. eliminates this entire class of bugs, eliminates a huge pile of
> exports, etc.
> 
>  : > Since the symbols in the new module are invisible outside, I recommend:
>  : > new kvm_intel.ko = kvm_intel.ko + kvm.ko
>  : > new kvm_amd.ko = kvm_amd.ko + kvm.ko
>  : 
>  : Yeah, Paolo also suggested this at LPC.
> 
> [*] https://lore.kernel.org/all/ZWYtDGH5p4RpGYBw@google.com
> 

+1.  This makes life a lot easier.