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

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Date:   Wed, 21 Jun 2017 08:54:57 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
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 6/21/2017 2:37 AM, Thomas Gleixner wrote:
> 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.

Ok, that sounds good.  I'll remove the check and usage of phys_to_virt()
and update the changelog with additional detail about that.

Thanks,
Tom

> 
> Thanks,
> 
> 	tglx
>