linux-kernel - Re: [PATCH RFC v7 06/64] KVM: x86: Add platform hooks for private memory invalidations

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Message-ID: <20230105022714.kdpybcse24xi2lq6@amd.com>
Date:   Wed, 4 Jan 2023 20:27:14 -0600
From:   Michael Roth <michael.roth@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     <kvm@...r.kernel.org>, <linux-coco@...ts.linux.dev>,
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Subject: Re: [PATCH RFC v7 06/64] KVM: x86: Add platform hooks for private
 memory invalidations

On Fri, Dec 30, 2022 at 12:53:31PM +0100, Borislav Petkov wrote:
> On Wed, Dec 14, 2022 at 01:39:58PM -0600, Michael Roth wrote:
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index a0c41d391547..2713632e5061 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -7183,3 +7183,8 @@ void kvm_arch_set_memory_attributes(struct kvm *kvm,
> >  		kvm_update_lpage_private_shared_mixed(kvm, slot, attrs,
> >  						      start, end);
> >  }
> > +
> > +void kvm_arch_invalidate_restricted_mem(struct kvm_memory_slot *slot, gfn_t start, gfn_t end)
> > +{
> > +	static_call_cond(kvm_x86_invalidate_restricted_mem)(slot, start, end);
> 
> Why _cond?

Since this hook is declared via KVM_X86_OP_OPTIONAL() (instead of
KVM_X86_OP_OPTIONAL_RET0 like the previous hooks), the comment in kvm-x86-ops.h
suggests this should be called via static_call_cond():

  /*
   * KVM_X86_OP() and KVM_X86_OP_OPTIONAL() are used to help generate
   * both DECLARE/DEFINE_STATIC_CALL() invocations and
   * "static_call_update()" calls.
   *
   * KVM_X86_OP_OPTIONAL() can be used for those functions that can have
   * a NULL definition, for example if "static_call_cond()" will be used
   * at the call sites.  KVM_X86_OP_OPTIONAL_RET0() can be used likewise
   * to make a definition optional, but in this case the default will
   * be __static_call_return0.
   */


> 
> > @@ -258,6 +263,17 @@ void restrictedmem_unregister_notifier(struct file *file,
> >  				       struct restrictedmem_notifier *notifier)
> >  {
> >  	struct restrictedmem_data *data = file->f_mapping->private_data;
> > +	struct inode *inode = file_inode(data->memfd);
> > +
> > +	/* TODO: this will issue notifications to all registered notifiers,
> 
> First of all:
> 
> verify_comment_style: WARNING: Multi-line comment needs to start text on the second line:
>  [+     /* TODO: this will issue notifications to all registered notifiers,]
> 
> Then, if you only want to run the callbacks for the one going away only,
> why don't you simply do:
> 
>         mutex_lock(&data->lock);
>         notifier->ops->invalidate_start(notifier, 0, inode->i_size >> PAGE_SHIFT);
>         notifier->ops->invalidate_end(notifier, 0, inode->i_size >> PAGE_SHIFT);
>         list_del(&notifier->list);
>         mutex_unlock(&data->lock);
> 
> here?

That should do the trick. Thanks for the suggestion.

-Mike

> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette