linux-kernel - Re: [PATCH] x86/mm: Fix PAGE_KERNEL

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Date:   Fri, 3 Dec 2021 10:48:18 -0800
From:   Lucas De Marchi <lucas.demarchi@...el.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Joerg Roedel <joro@...tes.org>, x86@...nel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, hpa@...or.com,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Brijesh Singh <brijesh.singh@....com>,
        linux-kernel@...r.kernel.org, Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH] x86/mm: Fix PAGE_KERNEL_IO removal breakage

On Fri, Dec 03, 2021 at 11:32:45AM -0600, Tom Lendacky wrote:
>On 12/3/21 11:28 AM, Tom Lendacky wrote:
>>On 12/2/21 6:25 PM, Lucas De Marchi wrote:
>>>On Thu, Dec 02, 2021 at 07:55:14AM -0800, Lucas De Marchi wrote:
>>>>On Thu, Dec 02, 2021 at 03:46:46PM +0100, Joerg Roedel wrote:
>>>>>From: Joerg Roedel <jroedel@...e.de>
>>>>>
>>>>>The removal of PAGE_KERNEL_IO broke SEV-ES because it changed the
>>>>>mapping of ioremap and some fixmap areas (like the local APIC page)
>>>>>from unencrypted to encrypted. Change those mappings back to
>>>>>be unencrypted.
>>>>>
>>>>>Cc: Lucas De Marchi <lucas.demarchi@...el.com>
>>>>>Fixes: 27dff0f58bde ("x86/mm: Nuke PAGE_KERNEL_IO")
>>>>>Signed-off-by: Joerg Roedel <jroedel@...e.de>
>>>>
>>>>oops, missed the fact PAGE_KERNEL had `| ENC` while PAGE_KERENL_IO
>>>>didn't have it. Thanks for the fixup.
>>>
>>>on a second thought, the fact that PAGE_KERNEL is _not_ the same as
>>>PAGE_KERNEL_IO, completely invalidates those 2 patches I sent. It seems
>>>I screwed it up big here.
>>>
>>>About the first patch,
>>>6b2a2138cf36 ("drm/i915/gem: Stop using PAGE_KERNEL_IO"),
>>>I didn't notice any regression on the i915
>>>side though. Is it safe to keep it? Otherwise we are probably better
>>>off reverting everything.
>
>Is i915 for just integrated graphics? In which case SME/SEV-ES aren't 
>available on Intel.

No, it's also for discrete graphics - so it could also be paired with an
AMD cpu.

Currently the i915 driver has some assumptions about the architecture
(x86/x86-64) since it used to be for integrated-only and thus Intel-only.
But we are now extending it to other architectures like arm64.  That's
why this patch was written: I misread PAGE_KERNEL and PAGE_KERNEL_IO
being the same thing nowadays, so I was switched to the one available in
other archs.

thanks
Lucas De Marchi

>
>Thanks,
>Tom
>
>>>
>>>I'm wondering why the addition of memory encryption
>>>in 21729f81ce8a ("x86/mm: Provide general kernel support for 
>>>memory encryption")
>>>didn't break io_mapping_init_wc() though as it had already done a
>>>s/PAGE_KERNEL_IO/PAGE_KERNEL/ in commit
>>>ac96b5566926 ("io-mapping.h: s/PAGE_KERNEL_IO/PAGE_KERNEL/")
>>
>>If I follow it correctly, since SME/SEV-ES are X86_64 only, 
>>io_mapping_init_wc() takes the ioremap_wc() path which uses 
>>PAGE_KERNEL_IO. iomap_create_wc() is only called when 
>>CONFIG_HAVE_ATOMIC_IOMAP is set, which isn't set for X86_64.
>>
>>Thanks,
>>Tom
>>
>>>
>>>thanks
>>>Lucas De Marchi
>>>
>>>>
>>>>Reviewed-by: Lucas De Marchi <lucas.demarchi@...el.com>
>>>>
>>>>Lucas De Marchi
>>>>
>>>>>---
>>>>>arch/x86/include/asm/fixmap.h        |  2 +-
>>>>>arch/x86/include/asm/pgtable_types.h | 21 +++++++++++----------
>>>>>arch/x86/mm/ioremap.c                |  2 +-
>>>>>3 files changed, 13 insertions(+), 12 deletions(-)
>>>>>
>>>>>diff --git a/arch/x86/include/asm/fixmap.h 
>>>>>b/arch/x86/include/asm/fixmap.h
>>>>>index 5e186a69db10..a2eaf265f784 100644
>>>>>--- a/arch/x86/include/asm/fixmap.h
>>>>>+++ b/arch/x86/include/asm/fixmap.h
>>>>>@@ -173,7 +173,7 @@ static inline void __set_fixmap(enum 
>>>>>fixed_addresses idx,
>>>>>* supported for MMIO addresses, so make sure that the memory encryption
>>>>>* mask is not part of the page attributes.
>>>>>*/
>>>>>-#define FIXMAP_PAGE_NOCACHE PAGE_KERNEL_NOCACHE
>>>>>+#define FIXMAP_PAGE_NOCACHE PAGE_KERNEL_NOCACHE_NOENC
>>>>>
>>>>>/*
>>>>>* Early memremap routines used for in-place encryption. The 
>>>>>mappings created
>>>>>diff --git a/arch/x86/include/asm/pgtable_types.h 
>>>>>b/arch/x86/include/asm/pgtable_types.h
>>>>>index a87224767ff3..fc9b6995cb22 100644
>>>>>--- a/arch/x86/include/asm/pgtable_types.h
>>>>>+++ b/arch/x86/include/asm/pgtable_types.h
>>>>>@@ -208,16 +208,17 @@ enum page_cache_mode {
>>>>>
>>>>>#define __pgprot_mask(x)    __pgprot((x) & __default_kernel_pte_mask)
>>>>>
>>>>>-#define PAGE_KERNEL        
>>>>>__pgprot_mask(__PAGE_KERNEL            | _ENC)
>>>>>-#define PAGE_KERNEL_NOENC    __pgprot_mask(__PAGE_KERNEL |    0)
>>>>>-#define PAGE_KERNEL_RO        __pgprot_mask(__PAGE_KERNEL_RO         
>>>>>| _ENC)
>>>>>-#define PAGE_KERNEL_EXEC    
>>>>>__pgprot_mask(__PAGE_KERNEL_EXEC       | _ENC)
>>>>>-#define PAGE_KERNEL_EXEC_NOENC 
>>>>>__pgprot_mask(__PAGE_KERNEL_EXEC       |    0)
>>>>>-#define PAGE_KERNEL_ROX        __pgprot_mask(__PAGE_KERNEL_ROX | _ENC)
>>>>>-#define PAGE_KERNEL_NOCACHE    
>>>>>__pgprot_mask(__PAGE_KERNEL_NOCACHE | _ENC)
>>>>>-#define PAGE_KERNEL_LARGE    
>>>>>__pgprot_mask(__PAGE_KERNEL_LARGE      | _ENC)
>>>>>-#define PAGE_KERNEL_LARGE_EXEC 
>>>>>__pgprot_mask(__PAGE_KERNEL_LARGE_EXEC | _ENC)
>>>>>-#define PAGE_KERNEL_VVAR    
>>>>>__pgprot_mask(__PAGE_KERNEL_VVAR       | _ENC)
>>>>>+#define PAGE_KERNEL            __pgprot_mask(__PAGE_KERNEL | _ENC)
>>>>>+#define PAGE_KERNEL_NOENC __pgprot_mask(__PAGE_KERNEL            |    0)
>>>>>+#define PAGE_KERNEL_RO __pgprot_mask(__PAGE_KERNEL_RO         | _ENC)
>>>>>+#define PAGE_KERNEL_EXEC        __pgprot_mask(__PAGE_KERNEL_EXEC | _ENC)
>>>>>+#define PAGE_KERNEL_EXEC_NOENC 
>>>>>__pgprot_mask(__PAGE_KERNEL_EXEC       |    0)
>>>>>+#define PAGE_KERNEL_ROX __pgprot_mask(__PAGE_KERNEL_ROX        | _ENC)
>>>>>+#define PAGE_KERNEL_NOCACHE 
>>>>>__pgprot_mask(__PAGE_KERNEL_NOCACHE    | _ENC)
>>>>>+#define PAGE_KERNEL_NOCACHE_NOENC 
>>>>>__pgprot_mask(__PAGE_KERNEL_NOCACHE    |    0)
>>>>>+#define PAGE_KERNEL_LARGE __pgprot_mask(__PAGE_KERNEL_LARGE      | _ENC)
>>>>>+#define PAGE_KERNEL_LARGE_EXEC 
>>>>>__pgprot_mask(__PAGE_KERNEL_LARGE_EXEC | _ENC)
>>>>>+#define PAGE_KERNEL_VVAR        __pgprot_mask(__PAGE_KERNEL_VVAR | _ENC)
>>>>>
>>>>>#endif    /* __ASSEMBLY__ */
>>>>>
>>>>>diff --git a/arch/x86/mm/ioremap.c b/arch/x86/mm/ioremap.c
>>>>>index 3102dda4b152..4fe8d43d53bb 100644
>>>>>--- a/arch/x86/mm/ioremap.c
>>>>>+++ b/arch/x86/mm/ioremap.c
>>>>>@@ -243,7 +243,7 @@ __ioremap_caller(resource_size_t 
>>>>>phys_addr, unsigned long size,
>>>>>     * make sure the memory encryption attribute is enabled in the
>>>>>     * resulting mapping.
>>>>>     */
>>>>>-    prot = PAGE_KERNEL;
>>>>>+    prot = PAGE_KERNEL_NOENC;
>>>>>    if ((io_desc.flags & IORES_MAP_ENCRYPTED) || encrypted)
>>>>>        prot = pgprot_encrypted(prot);
>>>>>
>>>>>-- 
>>>>>2.34.0
>>>>>