linux-kernel - Re: [PATCH v7 07/36] x86/mm: Don't use phys_to

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Date:   Wed, 21 Jun 2017 09:37:39 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Tom Lendacky <thomas.lendacky@....com>
cc:     linux-arch@...r.kernel.org, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com, xen-devel@...ts.xen.org,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Brijesh Singh <brijesh.singh@....com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Alexander Potapenko <glider@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Joerg Roedel <joro@...tes.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dave Young <dyoung@...hat.com>, Rik van Riel <riel@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Juergen Gross <jgross@...e.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v7 07/36] x86/mm: Don't use phys_to_virt in ioremap() if
 SME is active

On Fri, 16 Jun 2017, Tom Lendacky wrote:
> Currently there is a check if the address being mapped is in the ISA
> range (is_ISA_range()), and if it is then phys_to_virt() is used to
> perform the mapping.  When SME is active, however, this will result
> in the mapping having the encryption bit set when it is expected that
> an ioremap() should not have the encryption bit set. So only use the
> phys_to_virt() function if SME is not active
> 
> Reviewed-by: Borislav Petkov <bp@...e.de>
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> ---
>  arch/x86/mm/ioremap.c |    7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
> index 4c1b5fd..a382ba9 100644
> --- a/arch/x86/mm/ioremap.c
> +++ b/arch/x86/mm/ioremap.c
> @@ -13,6 +13,7 @@
>  #include <linux/slab.h>
>  #include <linux/vmalloc.h>
>  #include <linux/mmiotrace.h>
> +#include <linux/mem_encrypt.h>
>  
>  #include <asm/set_memory.h>
>  #include <asm/e820/api.h>
> @@ -106,9 +107,11 @@ static void __iomem *__ioremap_caller(resource_size_t phys_addr,
>  	}
>  
>  	/*
> -	 * Don't remap the low PCI/ISA area, it's always mapped..
> +	 * Don't remap the low PCI/ISA area, it's always mapped.
> +	 *   But if SME is active, skip this so that the encryption bit
> +	 *   doesn't get set.
>  	 */
> -	if (is_ISA_range(phys_addr, last_addr))
> +	if (is_ISA_range(phys_addr, last_addr) && !sme_active())
>  		return (__force void __iomem *)phys_to_virt(phys_addr);

More thoughts about that.

Making this conditional on !sme_active() is not the best idea. I'd rather
remove that whole thing and make it unconditional so the code pathes get
always exercised and any subtle wreckage is detected on a broader base and
not only on that hard to access and debug SME capable machine owned by Joe
User.

Thanks,

	tglx