linux-kernel - Re: [PATCH v2] KVM: x86: Don't read guest CR3 when doing async pf while the MMU is direct

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Message-ID: <aUB0wlJKtyyJTewL@google.com>
Date: Mon, 15 Dec 2025 12:51:14 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Xiaoyao Li <xiaoyao.li@...el.com>
Cc: kernel test robot <lkp@...el.com>, Paolo Bonzini <pbonzini@...hat.com>, oe-kbuild-all@...ts.linux.dev, 
	Rick Edgecombe <rick.p.edgecombe@...el.com>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org, farrah.chen@...el.com
Subject: Re: [PATCH v2] KVM: x86: Don't read guest CR3 when doing async pf
 while the MMU is direct

On Mon, Dec 15, 2025, Xiaoyao Li wrote:
> On 12/13/2025 9:01 AM, Sean Christopherson wrote:
> > On Sat, Dec 13, 2025, kernel test robot wrote:
> > > Hi Xiaoyao,
> > > 
> > > kernel test robot noticed the following build warnings:
> > > 
> > > [auto build test WARNING on 7d0a66e4bb9081d75c82ec4957c50034cb0ea449]
> > > 
> > > url:    https://github.com/intel-lab-lkp/linux/commits/Xiaoyao-Li/KVM-x86-Don-t-read-guest-CR3-when-doing-async-pf-while-the-MMU-is-direct/20251212-220612
> > > base:   7d0a66e4bb9081d75c82ec4957c50034cb0ea449
> > > patch link:    https://lore.kernel.org/r/20251212135051.2155280-1-xiaoyao.li%40intel.com
> > > patch subject: [PATCH v2] KVM: x86: Don't read guest CR3 when doing async pf while the MMU is direct
> > > config: i386-buildonly-randconfig-002-20251213 (https://download.01.org/0day-ci/archive/20251213/202512130717.aHH8rXSC-lkp@intel.com/config)
> > > compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
> > > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251213/202512130717.aHH8rXSC-lkp@intel.com/reproduce)
> > > 
> > > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > > the same patch/commit), kindly add following tags
> > > | Reported-by: kernel test robot <lkp@...el.com>
> > > | Closes: https://lore.kernel.org/oe-kbuild-all/202512130717.aHH8rXSC-lkp@intel.com/
> > > 
> > > All warnings (new ones prefixed by >>):
> > > 
> > >     In file included from include/linux/kvm_host.h:43,
> > >                      from arch/x86/kvm/irq.h:15,
> > >                      from arch/x86/kvm/mmu/mmu.c:19:
> > >     arch/x86/kvm/mmu/mmu.c: In function 'kvm_arch_setup_async_pf':
> > > > > include/linux/kvm_types.h:54:25: warning: conversion from 'long long unsigned int' to 'long unsigned int' changes value from '18446744073709551615' to '4294967295' [-Woverflow]
> > >        54 | #define INVALID_GPA     (~(gpa_t)0)
> > >           |                         ^
> > >     arch/x86/kvm/mmu/mmu.c:4525:28: note: in expansion of macro 'INVALID_GPA'
> > >      4525 |                 arch.cr3 = INVALID_GPA;
> > >           |                            ^~~~~~~~~~~
> > 
> > Well that's just annoying.  Can we kill 32-bit yet?  Anyways, just ignore this
> > (unless it causes my KVM_WERROR=1 builds to fail, in which case I'll just add an
> > explicit cast, but I think we can just ignore it).
> 
> If your KVM_WERROR=1 builds contain 32-bit config, I think it will fail. I
> think we do need to add the explicit cast.

Ya, you were right.

> You will handle it when applying, right? Thus no need for a v3.

Yep.