linux-kernel - [PATCH 1/2] x86/io: add interface to reserve io memtype for a resource range.

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Message-Id: <1477288304-6687-1-git-send-email-airlied@redhat.com>
Date:   Mon, 24 Oct 2016 15:51:43 +1000
From:   Dave Airlie <airlied@...hat.com>
To:     mcgrof@...e.com, torvalds@...ux-foundation.org,
        dan.j.williams@...el.com, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.sf.net,
        Dave Airlie <airlied@...hat.com>
Subject: [PATCH 1/2] x86/io: add interface to reserve io memtype for a resource range.

A recent change to the mm code in:
87744ab3832b83ba71b931f86f9cfdb000d07da5
mm: fix cache mode tracking in vm_insert_mixed()

started enforcing checking the memory type against the registered list for
amixed pfn insertion mappings. It happens that the drm drivers for a number
of gpus relied on this being broken. Currently the driver only inserted
VRAM mappings into the tracking table when they came from the kernel,
and userspace mappings never landed in the table. This led to a regression
where all the mapping end up as UC instead of WC now.

I've considered a number of solutions but since this needs to be fixed
in fixes and not next, and some of the solutions were going to introduce
overhead that hadn't been there before I didn't consider them viable at
this stage. These mainly concerned hooking into the TTM io reserve APIs,
but these API have a bunch of fast paths I didn't want to unwind to add
this to.

The solution I've decided on is to add a new API like the arch_phys_wc
APIs (these would have worked but wc_del didn't take a range), and
use them from the drivers to add a WC compatible mapping to the table
for all VRAM on those GPUs. This means we can then create userspace
mapping that won't get degraded to UC.

Signed-off-by: Dave Airlie <airlied@...hat.com>
---
 arch/x86/include/asm/io.h |  6 ++++++
 arch/x86/mm/pat.c         | 13 +++++++++++++
 include/linux/io.h        | 13 +++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/arch/x86/include/asm/io.h b/arch/x86/include/asm/io.h
index de25aad..6e18f66 100644
--- a/arch/x86/include/asm/io.h
+++ b/arch/x86/include/asm/io.h
@@ -351,4 +351,10 @@ extern void arch_phys_wc_del(int handle);
 #define arch_phys_wc_add arch_phys_wc_add
 #endif
 
+#ifdef CONFIG_PAT
+extern int arch_io_reserve_memtype_wc(resource_size_t start, resource_size_t size);
+extern void arch_io_free_memtype_wc(resource_size_t start, resource_size_t size);
+#define arch_io_reserve_memtype_wc arch_io_reserve_memtype_wc
+#endif
+
 #endif /* _ASM_X86_IO_H */
diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 170cc4f..49d1b75 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -730,6 +730,19 @@ void io_free_memtype(resource_size_t start, resource_size_t end)
 	free_memtype(start, end);
 }
 
+int arch_io_reserve_memtype_wc(resource_size_t start, resource_size_t size)
+{
+	enum page_cache_mode type = _PAGE_CACHE_MODE_WC;
+	return io_reserve_memtype(start, start + size, &type);
+}
+EXPORT_SYMBOL(arch_io_reserve_memtype_wc);
+
+void arch_io_free_memtype_wc(resource_size_t start, resource_size_t size)
+{
+	io_free_memtype(start, start + size);
+}
+EXPORT_SYMBOL(arch_io_free_memtype_wc);
+
 pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
 				unsigned long size, pgprot_t vma_prot)
 {
diff --git a/include/linux/io.h b/include/linux/io.h
index e2c8419..963ab71 100644
--- a/include/linux/io.h
+++ b/include/linux/io.h
@@ -141,4 +141,17 @@ enum {
 void *memremap(resource_size_t offset, size_t size, unsigned long flags);
 void memunmap(void *addr);
 
+#ifndef arch_io_reserve_memtype_wc
+static inline int arch_io_reserve_memtype_wc(resource_size_t base,
+					     resource_size_t size)
+{
+	return 0;
+}
+
+static inline void arch_io_free_memtype_wc(resource_size_t base,
+					   resource_size_t size)
+{
+}
+#endif
+
 #endif /* _LINUX_IO_H */
-- 
2.5.5