Re: [PATCH v10 21/45] x86/mm: Add support to validate memory when changing C-bit

[Brijesh Singh]

On 2/21/22 11:41, Kirill A. Shutemov wrote:
> On Wed, Feb 16, 2022 at 10:04:57AM -0600, Brijesh Singh wrote:
> > @@ -287,6 +301,7 @@ struct x86_platform_ops {
> >   	struct x86_legacy_features legacy;
> >   	void (*set_legacy_features)(void);
> >   	struct x86_hyper_runtime hyper;
> > +	struct x86_guest guest;
> >   };
>
> I used 'cc' instead of 'guest'. 'guest' looks too generic.

I am fine with either of them.

> Also, I'm not sure why not to use pointer to ops struct instead of stroing
> them directly in x86_platform. Yes, it is consistent with 'hyper', but I
> don't see it as a strong argument.
>
> >   
> > index b4072115c8ef..a55477a6e578 100644
> > --- a/arch/x86/mm/pat/set_memory.c
> > +++ b/arch/x86/mm/pat/set_memory.c
> > @@ -2012,8 +2012,15 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
> >   	 */
> >   	cpa_flush(&cpa, !this_cpu_has(X86_FEATURE_SME_COHERENT));
> >   
> > +	/* Notify HV that we are about to set/clr encryption attribute. */
> > +	x86_platform.guest.enc_status_change_prepare(addr, numpages, enc);
> > +
> >   	ret = __change_page_attr_set_clr(&cpa, 1);
>
> This doesn't cover difference in flushing requirements. Can we get it too?

Yes, we can work to include that too.

> >   
> > +	/* Notify HV that we have succesfully set/clr encryption attribute. */
> > +	if (!ret)
> > +		x86_platform.guest.enc_status_change_finish(addr, numpages, enc);
> > +
>
> Any particular reason you moved it above cpa_flush()? I don't think it
> makes a difference for TDX, but still.

It does not make any difference for the SNP as well. We can keep it 
where it was.


> >   	/*
> >   	 * After changing the encryption attribute, we need to flush TLBs again
> >   	 * in case any speculative TLB caching occurred (but no need to flush
> > @@ -2023,12 +2030,6 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
> >   	 */
> >   	cpa_flush(&cpa, 0);
> >   
> > -	/*
> > -	 * Notify hypervisor that a given memory range is mapped encrypted
> > -	 * or decrypted.
> > -	 */
> > -	notify_range_enc_status_changed(addr, numpages, enc);
> > -
> >   	return ret;
> >   }
> >   
> > --
> > 2.25.1