linux-kernel - Re: [RFC Part1 PATCH v3 15/17] x86: Add support for changing memory encryption attribute in early boot

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Date:   Mon, 28 Aug 2017 12:51:19 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-efi@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kvm@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Piotr Luc <piotr.luc@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        David Howells <dhowells@...hat.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Laura Abbott <labbott@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Jonathan Corbet <corbet@....net>,
        Dave Airlie <airlied@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Arnd Bergmann <arnd@...db.de>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>
Subject: Re: [RFC Part1 PATCH v3 15/17] x86: Add support for changing memory
 encryption attribute in early boot

On Mon, Jul 24, 2017 at 02:07:55PM -0500, Brijesh Singh wrote:
> Some KVM-specific custom MSRs shares the guest physical address with

s/shares/share/

> hypervisor.

"the hypervisor."

> When SEV is active, the shared physical address must be mapped
> with encryption attribute cleared so that both hypervsior and guest can
> access the data.
> 
> Add APIs to change memory encryption attribute in early boot code.
> 
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
>  arch/x86/include/asm/mem_encrypt.h |  17 ++++++
>  arch/x86/mm/mem_encrypt.c          | 117 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 134 insertions(+)

...

> +static int __init early_set_memory_enc_dec(resource_size_t paddr,
> +					   unsigned long size, bool enc)
> +{
> +	unsigned long vaddr, vaddr_end, vaddr_next;
> +	unsigned long psize, pmask;
> +	int split_page_size_mask;
> +	pte_t *kpte;
> +	int level;
> +
> +	vaddr = (unsigned long)__va(paddr);
> +	vaddr_next = vaddr;
> +	vaddr_end = vaddr + size;
> +
> +	/*
> +	 * We are going to change the physical page attribute from C=1 to C=0
> +	 * or vice versa. Flush the caches to ensure that data is written into
> +	 * memory with correct C-bit before we change attribute.
> +	 */
> +	clflush_cache_range(__va(paddr), size);
> +
> +	for (; vaddr < vaddr_end; vaddr = vaddr_next) {
> +		kpte = lookup_address(vaddr, &level);
> +		if (!kpte || pte_none(*kpte))
> +			return 1;

Return before flushing TLBs? Perhaps you mean

			ret = 1;
			goto out;

here and out does

	__flush_tlb_all();
	return ret;

?

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--