linux-kernel - Re: [PATCH, RFC 18/62] x86/mm: Implement syncing per-KeyID direct mappings

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Date:   Mon, 17 Jun 2019 18:17:17 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...capital.net>,
        David Howells <dhowells@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Kai Huang <kai.huang@...ux.intel.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Alison Schofield <alison.schofield@...el.com>,
        linux-mm@...ck.org, kvm@...r.kernel.org, keyrings@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH, RFC 18/62] x86/mm: Implement syncing per-KeyID direct
 mappings

On Mon, Jun 17, 2019 at 04:51:58PM +0200, Peter Zijlstra wrote:
> On Mon, Jun 17, 2019 at 05:43:28PM +0300, Kirill A. Shutemov wrote:
> > On Mon, Jun 17, 2019 at 11:27:55AM +0200, Peter Zijlstra wrote:
> 
> > > > > And yet I don't see anything in pageattr.c.
> > > > 
> > > > You're right. I've hooked up the sync in the wrong place.
> 
> > I think something like this should do (I'll fold it in after testing):
> 
> > @@ -643,7 +641,7 @@ static int sync_direct_mapping_keyid(unsigned long keyid)
> >   *
> >   * The function is nop until MKTME is enabled.
> >   */
> > -int sync_direct_mapping(void)
> > +int sync_direct_mapping(unsigned long start, unsigned long end)
> >  {
> >  	int i, ret = 0;
> >  
> > @@ -651,7 +649,7 @@ int sync_direct_mapping(void)
> >  		return 0;
> >  
> >  	for (i = 1; !ret && i <= mktme_nr_keyids; i++)
> > -		ret = sync_direct_mapping_keyid(i);
> > +		ret = sync_direct_mapping_keyid(i, start, end);
> >  
> >  	flush_tlb_all();
> >  
> > diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> > index 6a9a77a403c9..eafbe0d8c44f 100644
> > --- a/arch/x86/mm/pageattr.c
> > +++ b/arch/x86/mm/pageattr.c
> > @@ -347,6 +347,28 @@ static void cpa_flush(struct cpa_data *data, int cache)
> >  
> >  	BUG_ON(irqs_disabled() && !early_boot_irqs_disabled);
> >  
> > +	if (mktme_enabled()) {
> > +		unsigned long start, end;
> > +
> > +		start = *cpa->vaddr;
> > +		end = *cpa->vaddr + cpa->numpages * PAGE_SIZE;
> > +
> > +		/* Sync all direct mapping for an array */
> > +		if (cpa->flags & CPA_ARRAY) {
> > +			start = PAGE_OFFSET;
> > +			end = PAGE_OFFSET + direct_mapping_size;
> > +		}
> 
> Understandable but sad, IIRC that's the most used interface (at least,
> its the one the graphics people use).
> 
> > +
> > +		/*
> > +		 * Sync per-KeyID direct mappings with the canonical one
> > +		 * (KeyID-0).
> > +		 *
> > +		 * sync_direct_mapping() does full TLB flush.
> > +		 */
> > +		sync_direct_mapping(start, end);
> > +		return;
> 
> But it doesn't flush cache. So you can't return here.

Thanks for catching this.

	if (!cache)
		return;

should be fine.

-- 
 Kirill A. Shutemov