linux-kernel - Re: [PATCH v8 12/40] x86/sev: Add helper for validating pages in early enc attribute changes

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Message-ID: <YdOGk5b0vYSpP1Ws@dt>
Date:   Mon, 3 Jan 2022 17:28:19 -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 12/40] x86/sev: Add helper for validating pages in
 early enc attribute changes

On 2021-12-10 09:43:04 -0600, Brijesh Singh wrote:
> The early_set_memory_{encrypt,decrypt}() are used for changing the

s/encrypt,decrypt/encrypted,decrypted/

> page from decrypted (shared) to encrypted (private) and vice versa.
> When SEV-SNP is active, the page state transition needs to go through
> additional steps.
> 
> If the page is transitioned from shared to private, then perform the
> following after the encryption attribute is set in the page table:
> 
> 1. Issue the page state change VMGEXIT to add the page as a private
>    in the RMP table.
> 2. Validate the page after its successfully added in the RMP table.
> 
> To maintain the security guarantees, if the page is transitioned from
> private to shared, then perform the following before clearing the
> encryption attribute from the page table.
> 
> 1. Invalidate the page.
> 2. Issue the page state change VMGEXIT to make the page shared in the
>    RMP table.
> 
> The early_set_memory_{encrypt,decrypt} can be called before the GHCB

s/encrypt,decrypt/encrypted,decrypted/

> is setup, use the SNP page state MSR protocol VMGEXIT defined in the GHCB
> specification to request the page state change in the RMP table.
> 
> While at it, add a helper snp_prep_memory() that can be used outside
> the sev specific files to change the page state for a specified memory
> range.
> 
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>

And with a few other nits below:

Reviewed-by: Venu Busireddy <venu.busireddy@...cle.com>

> diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
> +
> +	 /*
> +	  * Ask the hypervisor to mark the memory pages as private in the RMP
> +	  * table.
> +	  */

Indentation is off. While at it, you may want to collapse it into a one
line comment.

> +	early_set_page_state(paddr, npages, SNP_PAGE_STATE_PRIVATE);
> +
> +	/* Validate the memory pages after they've been added in the RMP table. */
> +	pvalidate_pages(vaddr, npages, 1);
> +}
> +
> +void __init early_snp_set_memory_shared(unsigned long vaddr, unsigned long paddr,
> +					unsigned int npages)
> +{
> +	if (!cc_platform_has(CC_ATTR_SEV_SNP))
> +		return;
> +
> +	/*
> +	 * Invalidate the memory pages before they are marked shared in the
> +	 * RMP table.
> +	 */

Collapse into one line?

> +	pvalidate_pages(vaddr, npages, 0);
> +
> +	 /* Ask hypervisor to mark the memory pages shared in the RMP table. */

Indentation is off.

> +		/*
> +		 * ON SNP, the page state in the RMP table must happen
> +		 * before the page table updates.
> +		 */
> +		early_snp_set_memory_shared((unsigned long)__va(pa), pa, 1);

I know "1" implies "true", but to emphasize that the argument is
actually a boolean, could you please change the "1" to "true?"

> +	}
> +
>  	/* Change the page encryption mask. */
>  	new_pte = pfn_pte(pfn, new_prot);
>  	set_pte_atomic(kpte, new_pte);
> +
> +	/*
> +	 * If page is set encrypted in the page table, then update the RMP table to
> +	 * add this page as private.
> +	 */
> +	if (enc)
> +		early_snp_set_memory_private((unsigned long)__va(pa), pa, 1);

Here too, could you please change the "1" to "true?"

Venu