linux-kernel - Re: [PATCH v8 09/40] x86/compressed: Add helper for validating pages in the decompression stage

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Message-ID: <YdND4m/XjX6tRo0z@dt>
Date:   Mon, 3 Jan 2022 12:43:46 -0600
From:   Venu Busireddy <venu.busireddy@...cle.com>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v8 09/40] x86/compressed: Add helper for validating pages
 in the decompression stage

On 2021-12-17 17:24:43 -0600, Brijesh Singh wrote:
> 
> On 12/17/21 2:47 PM, Venu Busireddy wrote:
> 
> >>  	 * the caches.
> >>  	 */
> >> -	if ((set | clr) & _PAGE_ENC)
> >> +	if ((set | clr) & _PAGE_ENC) {
> >>  		clflush_page(address);
> >>  
> >> +		/*
> >> +		 * If the encryption attribute is being cleared, then change
> >> +		 * the page state to shared in the RMP table.
> >> +		 */
> >> +		if (clr)
> > This function is also called by set_page_non_present() with clr set to
> > _PAGE_PRESENT. Do we want to change the page state to shared even when
> > the page is not present? If not, shouldn't the check be (clr & _PAGE_ENC)?
> 
> I am not able to follow your comment. Here we only pay attention to the
> encryption attribute, if encryption attribute is getting cleared then
> make PSC. In the case ov set_page_non_present(), the outer if() block
> will return false.  Am I missing something ?

You are right. I missed the outer check.

> > The page is not "added", right? Shouldn't we just say:
> 
> Technically, PSC modifies the RMP entry, so I should use that  instead
> of calling "added".
> 
> 
> >     Validate the page so that it is consistent with the RMP entry.
> 
> Yes, I am okay with it.

Thanks,

Venu