linux-kernel - Re: [PATCH Part2 v5 08/45] x86/fault: Add support to handle the RMP fault for user address

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Message-ID: <YVSuMUk7Aq0hIl1h@zn.tnic>
Date:   Wed, 29 Sep 2021 20:19:29 +0200
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-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.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>,
        Wanpeng Li <wanpengli@...cent.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>, tony.luck@...el.com,
        marcorr@...gle.com, sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH Part2 v5 08/45] x86/fault: Add support to handle the RMP
 fault for user address

On Fri, Aug 20, 2021 at 10:58:41AM -0500, Brijesh Singh wrote:
> +static int handle_user_rmp_page_fault(struct pt_regs *regs, unsigned long error_code,
> +				      unsigned long address)
> +{

#ifdef CONFIG_AMD_MEM_ENCRYPT

> +	int rmp_level, level;
> +	pte_t *pte;
> +	u64 pfn;
> +
> +	pte = lookup_address_in_mm(current->mm, address, &level);
> +
> +	/*
> +	 * It can happen if there was a race between an unmap event and
> +	 * the RMP fault delivery.
> +	 */
> +	if (!pte || !pte_present(*pte))
> +		return 1;
> +
> +	pfn = pte_pfn(*pte);
> +
> +	/* If its large page then calculte the fault pfn */
> +	if (level > PG_LEVEL_4K) {
> +		unsigned long mask;
> +
> +		mask = pages_per_hpage(level) - pages_per_hpage(level - 1);

Just use two helper variables named properly instead of this oneliner:

		pages_level 	 = page_level_size(level) / PAGE_SIZE;
		pages_prev_level = page_level_size(level - 1) / PAGE_SIZE;

> +		pfn |= (address >> PAGE_SHIFT) & mask;
> +	}
> +
> +	/*
> +	 * If its a guest private page, then the fault cannot be resolved.
> +	 * Send a SIGBUS to terminate the process.
> +	 */
> +	if (snp_lookup_rmpentry(pfn, &rmp_level)) {
> +		do_sigbus(regs, error_code, address, VM_FAULT_SIGBUS);
> +		return 1;
> +	}
> +
> +	/*
> +	 * The backing page level is higher than the RMP page level, request
> +	 * to split the page.
> +	 */
> +	if (level > rmp_level)
> +		return 0;
> +
> +	return 1;

#else
	WARN_ONONCE(1);
	return -1;
#endif

and also handle that -1 negative value at the call site.

Thx.

-- 
Regards/Gruss,
    Boris.

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