linux-kernel - Re: [PATCH v9 07/38] x86/mm: Remove phys_to

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Message-ID: <4404cf23-3b9c-e712-f883-fa6dc4318214@amd.com>
Date:   Tue, 11 Jul 2017 10:44:34 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Brian Gerst <brgerst@...il.com>
Cc:     linux-arch <linux-arch@...r.kernel.org>, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org,
        the arch/x86 maintainers <x86@...nel.org>,
        kexec@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kasan-dev <kasan-dev@...glegroups.com>, xen-devel@...ts.xen.org,
        Linux-MM <linux-mm@...ck.org>,
        "open list:IOMMU DRIVERS" <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>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v9 07/38] x86/mm: Remove phys_to_virt() usage in ioremap()

On 7/11/2017 10:38 AM, Brian Gerst wrote:
> On Tue, Jul 11, 2017 at 11:02 AM, Tom Lendacky <thomas.lendacky@....com> wrote:
>> On 7/10/2017 11:58 PM, Brian Gerst wrote:
>>>
>>> On Mon, Jul 10, 2017 at 3:50 PM, Tom Lendacky <thomas.lendacky@....com>
>>> wrote:
>>>>
>>>> On 7/8/2017 7:57 AM, Brian Gerst wrote:
>>>>>
>>>>>
>>>>> On Fri, Jul 7, 2017 at 9:39 AM, Tom Lendacky <thomas.lendacky@....com>
>>>>> 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, the default is to add
>>>>>> pagetable
>>>>>> mappings with the encryption bit set unless specifically overridden.
>>>>>> The
>>>>>> resulting pagetable mapping from phys_to_virt() will result in a
>>>>>> mapping
>>>>>> that has the encryption bit set. With SME, the use of ioremap() is
>>>>>> intended to generate pagetable mappings that do not have the encryption
>>>>>> bit set through the use of the PAGE_KERNEL_IO protection value.
>>>>>>
>>>>>> Rather than special case the SME scenario, remove the ISA range check
>>>>>> and
>>>>>> usage of phys_to_virt() and have ISA range mappings continue through
>>>>>> the
>>>>>> remaining ioremap() path.
>>>>>>
>>>>>> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
>>>>>> ---
>>>>>>     arch/x86/mm/ioremap.c |    7 +------
>>>>>>     1 file changed, 1 insertion(+), 6 deletions(-)
>>>>>>
>>>>>> diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
>>>>>> index 4c1b5fd..bfc3e2d 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>
>>>>>> @@ -106,12 +107,6 @@ static void __iomem
>>>>>> *__ioremap_caller(resource_size_t phys_addr,
>>>>>>            }
>>>>>>
>>>>>>            /*
>>>>>> -        * Don't remap the low PCI/ISA area, it's always mapped..
>>>>>> -        */
>>>>>> -       if (is_ISA_range(phys_addr, last_addr))
>>>>>> -               return (__force void __iomem *)phys_to_virt(phys_addr);
>>>>>> -
>>>>>> -       /*
>>>>>>             * Don't allow anybody to remap normal RAM that we're using..
>>>>>>             */
>>>>>>            pfn      = phys_addr >> PAGE_SHIFT;
>>>>>>
>>>>>
>>>>> Removing this also affects 32-bit, which is more likely to access
>>>>> legacy devices in this range.  Put in a check for SME instead
>>>>
>>>>
>>>>
>>>> I originally had a check for SME here in a previous version of the
>>>> patch.  Thomas Gleixner recommended removing the check so that the code
>>>> path was always exercised regardless of the state of SME in order to
>>>> better detect issues:
>>>>
>>>> http://marc.info/?l=linux-kernel&m=149803067811436&w=2
>>>>
>>>> Thanks,
>>>> Tom
>>>
>>>
>>> Looking a bit closer, this shortcut doesn't set the caching
>>> attributes.  So it's probably best to get rid of it anyways.  Also
>>> note, there is a corresponding check in iounmap().
>>
>>
>> Good catch.  I'll update the patch to include the removal of the ISA
>> checks in the iounmap() path as well.
> 
> I now think it should be kept but also emit a warning, at least for
> the short term.  There is bad code out there (vga16fb for example)
> that calls iounmap() blindly without calling ioremap() first.  We
> don't want to actually follow through with the unmap on the linear
> mapping.

Yup, was just about to reply to the other email on this. That makes
sense, keep the check but add a warning to it so that it will catch
any misuses of iounmap() and those can then be addressed.

Thanks,
Tom

> 
> --
> Brian Gerst
>