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

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Date:   Tue, 21 Dec 2021 14:01:26 +0100
From:   Borislav Petkov <bp@...en8.de>
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>,
        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 Fri, Dec 10, 2021 at 09:43:01AM -0600, Brijesh Singh wrote:
> diff --git a/arch/x86/boot/compressed/ident_map_64.c b/arch/x86/boot/compressed/ident_map_64.c
> index f7213d0943b8..ef77453cc629 100644
> --- a/arch/x86/boot/compressed/ident_map_64.c
> +++ b/arch/x86/boot/compressed/ident_map_64.c
> @@ -275,15 +275,31 @@ static int set_clr_page_flags(struct x86_mapping_info *info,
>  	 * Changing encryption attributes of a page requires to flush it from
>  	 * 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)
> +			snp_set_page_shared(pte_pfn(*ptep) << PAGE_SHIFT);

You forgot to change that one.

> +	}
> +
>  	/* Update PTE */
>  	pte = *ptep;
>  	pte = pte_set_flags(pte, set);
>  	pte = pte_clear_flags(pte, clr);
>  	set_pte(ptep, pte);
>  
> +	/*
> +	 * If the encryption attribute is being set, then change the page state to
> +	 * private in the RMP entry. The page state must be done after the PTE
                                                   ^
                                                 change

Geez, tell me, why should I be even bothering to review stuff if I have
to go look at the previous review I did and find that you haven't really
addressed it?!

> diff --git a/arch/x86/include/asm/sev-common.h b/arch/x86/include/asm/sev-common.h
> index 7ac5842e32b6..a2f956cfafba 100644
> --- a/arch/x86/include/asm/sev-common.h
> +++ b/arch/x86/include/asm/sev-common.h
> @@ -57,6 +57,32 @@
>  #define GHCB_MSR_AP_RESET_HOLD_REQ	0x006
>  #define GHCB_MSR_AP_RESET_HOLD_RESP	0x007
>  
> +/*
> + * SNP Page State Change Operation
> + *
> + * GHCBData[55:52] - Page operation:
> + *   0x0001 – Page assignment, Private
> + *   0x0002 – Page assignment, Shared

I wonder how you've achieved that:

massage_diff: Warning: Unicode char [–] (0x2013) in line: + *   0x0001 – Page assignment, Private
massage_diff: Warning: Unicode char [–] (0x2013) in line: + *   0x0002 – Page assignment, Shared

See https://trojansource.codes/ for some background.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette