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

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Message-ID: <20220221174121.ceeplpoaz63q72kv@box>
Date:   Mon, 21 Feb 2022 20:41:21 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     Borislav Petkov <bp@...en8.de>, 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>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        brijesh.ksingh@...il.com, tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v10 21/45] x86/mm: Add support to validate memory when
 changing C-bit

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.

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?

>  
> +	/* 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.

>  	/*
>  	 * 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
> 

-- 
 Kirill A. Shutemov