linux-kernel - Re: [RFC PATCH 13/39] KVM: guest_memfd: Make guest mem use guest mem inodes instead of anonymous inodes

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Message-ID: <aAm1utyxYWAowbPD@yzhao56-desk.sh.intel.com>
Date: Thu, 24 Apr 2025 11:53:30 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Ackerley Tng <ackerleytng@...gle.com>
CC: <tabba@...gle.com>, <quic_eberman@...cinc.com>, <roypat@...zon.co.uk>,
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Subject: Re: [RFC PATCH 13/39] KVM: guest_memfd: Make guest mem use guest mem
 inodes instead of anonymous inodes

On Wed, Apr 23, 2025 at 01:22:00PM -0700, Ackerley Tng wrote:
> Yan Zhao <yan.y.zhao@...el.com> writes:
> 
> > Hi Ackerley,
> >
> > Not sure if below nits have been resolved in your latest code.
> > I came across them and felt it's better to report them anyway.
> >
> > Apologies for any redundancy if you've already addressed them.
> 
> No worries, thank you so much for your reviews!
> 
> >
> > On Tue, Sep 10, 2024 at 11:43:44PM +0000, Ackerley Tng wrote:
> >> +static void kvm_gmem_init_mount(void)                                         
> >> +{                                                                             
> >> +     kvm_gmem_mnt = kern_mount(&kvm_gmem_fs);                                 
> >> +     BUG_ON(IS_ERR(kvm_gmem_mnt));                                            
> >> +                                                                              
> >> +     /* For giggles. Userspace can never map this anyways. */                 
> >> +     kvm_gmem_mnt->mnt_flags |= MNT_NOEXEC;                                   
> >> +}                                                                             
> >> +                                                                              
> >>  static struct file_operations kvm_gmem_fops = {                               
> >>       .open           = generic_file_open,                                     
> >>       .release        = kvm_gmem_release,                                      
> >> @@ -311,6 +348,8 @@ static struct file_operations kvm_gmem_fops = {            
> >>  void kvm_gmem_init(struct module *module)                                     
> >>  {                                                                             
> >>       kvm_gmem_fops.owner = module;                                            
> >> +                                                                              
> >> +     kvm_gmem_init_mount();                                                   
> >>  } 
> > When KVM is compiled as a module, looks "kern_unmount(kvm_gmem_mnt)" is
> > missing in the kvm_exit() path.
> >
> > This may lead to kernel oops when executing "sync" after KVM is unloaded or
> > reloaded.
> >
> 
> Thanks, Fuad will be addressing this in a revision of [1].
> 
> > BTW, there're lots of symbols not exported under mm.
> >
> 
> Thanks again, is there a good way to do a build test for symbols not
> being exported?  What CONFIG flags do you use?
I compiled kvm.ko and kvm-intel.ko as modules.

CONFIG_KVM=m
CONFIG_KVM_INTEL=m
CONFIG_KVM_INTEL_TDX=y