[PATCH RFC 0/2] Linux: possible ixes for mapping high MMIO regions

[PATCH RFC 0/2] Linux: possible ixes for mapping high MMIO regions

[David Vrabel]

This a possible fix for the problems with mapping high MMIO regions in
certain cases (e.g., the RDMA drivers) as not all mappers were
specifing the _PAGE_IOMAP which meant no valid MFN could be found and
the resulting PTE would be marked as not present, causing subsequent
faults.

It assumes that anything that isn't RAM (whether ballooned out or not)
is an I/O region and thus should be 1:1 in the p2m.  Ballooned frames
are still marked as missing in the p2m as before.

As a follow on, mfn_to_pfn() is (hopefully) extended to do the right
thing with such an MFN.  This means the Xen-specific _PAGE_IOMAP PTE
flag can be removed,

This series is posted as an early RFC in the hope that is an
acceptable approach.  It has only seen the bare minimum of smoke
testing (my test dom0 didn't explode). In particular, I've not
actually tested it with a device with a high MMIO.

David

[PATCH 1/2] x86/xen: set regions above the end of RAM as 1:1

[David Vrabel]

From: David Vrabel <david.vrabel@citrix.com>

PCI devices may have BARs located above the end of RAM so mark such
frames as identity frames in the p2m (instead of the default of
missing).

PFNs outside the p2m (above MAX_P2M_PFN) are also considered to be
identity frames for the same reason.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
 arch/x86/xen/p2m.c   |    2 +-
 arch/x86/xen/setup.c |   10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 2ae8699..a905355 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -481,7 +481,7 @@ unsigned long get_phys_to_machine(unsigned long pfn)
 	unsigned topidx, mididx, idx;
 
 	if (unlikely(pfn >= MAX_P2M_PFN))
-		return INVALID_P2M_ENTRY;
+		return IDENTITY_FRAME(pfn);
 
 	topidx = p2m_top_index(pfn);
 	mididx = p2m_mid_index(pfn);
diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
index 68c054f..6d7798f 100644
--- a/arch/x86/xen/setup.c
+++ b/arch/x86/xen/setup.c
@@ -412,6 +412,16 @@ char * __init xen_memory_setup(void)
 		max_pfn = min(MAX_DOMAIN_PAGES, last_pfn);
 		mem_end = PFN_PHYS(max_pfn);
 	}
+
+	/*
+	 * Set the rest as identity mapped, in case PCI BARs are
+	 * located here.
+	 *
+	 * PFNs above MAX_P2M_PFN are considered identity mapped as
+	 * well.
+	 */
+	set_phys_range_identity(max_pfn + 1, ~0ul);
+
 	/*
 	 * Clamp the amount of extra memory to a EXTRA_MEM_RATIO
 	 * factor the base size.  On non-highmem systems, the base
-- 
1.7.2.5

[PATCH 2/2] x86/xen: make mfn_to_pfn() work with MFNs that are 1:1 in the p2m

[David Vrabel]

From: David Vrabel <david.vrabel@citrix.com>

The _PAGE_IOMAP PTE flag is used to indicate that the PTE contains an
MFN that is an identify frame (1:1) in the p2m.  This is so the
correct conversion of MFN to PFN can be done reading a PTE.

If mfn_to_pfn() returned the correct PFN instead the _PAGE_IOMAP flag
is not required and can be removed.

In mfn_to_pfn() the PFN found in the M2P is checked in P2M.  If the
two MFNs differ then the MFN is one of three possibilities:

  a) its a foreign MFN with an m2p override.

  b) it's a foreign MFN with /no/ m2p override.

  c) it's a identity MFN.

It is not permitted to call mfn_to_pfn() no a foreign MFN without an
override was the resulting PFN will not incorrect.  We can therefore
assume case (c) and return PFN == MFN.

[ This patch should probably be split into the Xen-specific parts and
an x86 patch to remove _PAGE_IOMAP. ]

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
 arch/x86/include/asm/pgtable_types.h |   12 +++---
 arch/x86/include/asm/xen/page.h      |   18 +++++++---
 arch/x86/mm/init_32.c                |    2 +-
 arch/x86/mm/init_64.c                |    2 +-
 arch/x86/pci/i386.c                  |    2 -
 arch/x86/xen/enlighten.c             |    2 -
 arch/x86/xen/mmu.c                   |   58 +++++-----------------------------
 7 files changed, 28 insertions(+), 68 deletions(-)

diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
index 0ecac25..0b12657 100644
--- a/arch/x86/include/asm/pgtable_types.h
+++ b/arch/x86/include/asm/pgtable_types.h
@@ -17,7 +17,7 @@
 #define _PAGE_BIT_PAT		7	/* on 4KB pages */
 #define _PAGE_BIT_GLOBAL	8	/* Global TLB entry PPro+ */
 #define _PAGE_BIT_UNUSED1	9	/* available for programmer */
-#define _PAGE_BIT_IOMAP		10	/* flag used to indicate IO mapping */
+#define _PAGE_BIT_UNUSED2	10	/* available for programmer */
 #define _PAGE_BIT_HIDDEN	11	/* hidden by kmemcheck */
 #define _PAGE_BIT_PAT_LARGE	12	/* On 2MB or 1GB pages */
 #define _PAGE_BIT_SPECIAL	_PAGE_BIT_UNUSED1
@@ -41,7 +41,7 @@
 #define _PAGE_PSE	(_AT(pteval_t, 1) << _PAGE_BIT_PSE)
 #define _PAGE_GLOBAL	(_AT(pteval_t, 1) << _PAGE_BIT_GLOBAL)
 #define _PAGE_UNUSED1	(_AT(pteval_t, 1) << _PAGE_BIT_UNUSED1)
-#define _PAGE_IOMAP	(_AT(pteval_t, 1) << _PAGE_BIT_IOMAP)
+#define _PAGE_UNUSED2	(_AT(pteval_t, 1) << _PAGE_BIT_UNUSED2)
 #define _PAGE_PAT	(_AT(pteval_t, 1) << _PAGE_BIT_PAT)
 #define _PAGE_PAT_LARGE (_AT(pteval_t, 1) << _PAGE_BIT_PAT_LARGE)
 #define _PAGE_SPECIAL	(_AT(pteval_t, 1) << _PAGE_BIT_SPECIAL)
@@ -163,10 +163,10 @@
 #define __PAGE_KERNEL_LARGE_NOCACHE	(__PAGE_KERNEL | _PAGE_CACHE_UC | _PAGE_PSE)
 #define __PAGE_KERNEL_LARGE_EXEC	(__PAGE_KERNEL_EXEC | _PAGE_PSE)
 
-#define __PAGE_KERNEL_IO		(__PAGE_KERNEL | _PAGE_IOMAP)
-#define __PAGE_KERNEL_IO_NOCACHE	(__PAGE_KERNEL_NOCACHE | _PAGE_IOMAP)
-#define __PAGE_KERNEL_IO_UC_MINUS	(__PAGE_KERNEL_UC_MINUS | _PAGE_IOMAP)
-#define __PAGE_KERNEL_IO_WC		(__PAGE_KERNEL_WC | _PAGE_IOMAP)
+#define __PAGE_KERNEL_IO		(__PAGE_KERNEL)
+#define __PAGE_KERNEL_IO_NOCACHE	(__PAGE_KERNEL_NOCACHE)
+#define __PAGE_KERNEL_IO_UC_MINUS	(__PAGE_KERNEL_UC_MINUS)
+#define __PAGE_KERNEL_IO_WC		(__PAGE_KERNEL_WC)
 
 #define PAGE_KERNEL			__pgprot(__PAGE_KERNEL)
 #define PAGE_KERNEL_RO			__pgprot(__PAGE_KERNEL_RO)
diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
index b913915..eb11963 100644
--- a/arch/x86/include/asm/xen/page.h
+++ b/arch/x86/include/asm/xen/page.h
@@ -112,11 +112,18 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
 	pfn = mfn_to_pfn_no_overrides(mfn);
 	if (get_phys_to_machine(pfn) != mfn) {
 		/*
-		 * If this appears to be a foreign mfn (because the pfn
-		 * doesn't map back to the mfn), then check the local override
-		 * table to see if there's a better pfn to use.
+		 * This is either:
 		 *
-		 * m2p_find_override_pfn returns ~0 if it doesn't find anything.
+		 * a) a foreign MFN with an override.
+		 *
+		 * b) a foreign MFN without an override.
+		 *
+		 * c) an identity MFN that is not in the the p2m.
+		 *
+		 * For (a), look in the m2p overrides.  For (b) and
+		 * (c) assume identify MFN since mfn_to_pfn() will
+		 * only be called on foreign MFNs iff they have
+		 * overrides.
 		 */
 		pfn = m2p_find_override_pfn(mfn, ~0);
 	}
@@ -126,8 +133,7 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
 	 * entry doesn't map back to the mfn and m2p_override doesn't have a
 	 * valid entry for it.
 	 */
-	if (pfn == ~0 &&
-			get_phys_to_machine(mfn) == IDENTITY_FRAME(mfn))
+	if (pfn == ~0)
 		pfn = mfn;
 
 	return pfn;
diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
index 4287f1f..9031593 100644
--- a/arch/x86/mm/init_32.c
+++ b/arch/x86/mm/init_32.c
@@ -537,7 +537,7 @@ static void __init pagetable_init(void)
 	permanent_kmaps_init(pgd_base);
 }
 
-pteval_t __supported_pte_mask __read_mostly = ~(_PAGE_NX | _PAGE_GLOBAL | _PAGE_IOMAP);
+pteval_t __supported_pte_mask __read_mostly = ~(_PAGE_NX | _PAGE_GLOBAL);
 EXPORT_SYMBOL_GPL(__supported_pte_mask);
 
 /* user-defined highmem size */
diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
index 104d56a..68bf948 100644
--- a/arch/x86/mm/init_64.c
+++ b/arch/x86/mm/init_64.c
@@ -151,7 +151,7 @@ early_param("gbpages", parse_direct_gbpages_on);
  * around without checking the pgd every time.
  */
 
-pteval_t __supported_pte_mask __read_mostly = ~_PAGE_IOMAP;
+pteval_t __supported_pte_mask __read_mostly = ~0;
 EXPORT_SYMBOL_GPL(__supported_pte_mask);
 
 int force_personality32;
diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c
index db6b1ab..1f642d6 100644
--- a/arch/x86/pci/i386.c
+++ b/arch/x86/pci/i386.c
@@ -433,8 +433,6 @@ int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
 		 */
 		prot |= _PAGE_CACHE_UC_MINUS;
 
-	prot |= _PAGE_IOMAP;	/* creating a mapping for IO */
-
 	vma->vm_page_prot = __pgprot(prot);
 
 	if (io_remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index fa6ade7..f9c2d71 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -1458,8 +1458,6 @@ asmlinkage void __init xen_start_kernel(void)
 #endif
 		__supported_pte_mask &= ~(_PAGE_PWT | _PAGE_PCD);
 
-	__supported_pte_mask |= _PAGE_IOMAP;
-
 	/*
 	 * Prevent page tables from being allocated in highmem, even
 	 * if CONFIG_HIGHPTE is enabled.
diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index ce563be..5fa77a1 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -368,11 +368,9 @@ static pteval_t pte_mfn_to_pfn(pteval_t val)
 	if (val & _PAGE_PRESENT) {
 		unsigned long mfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
 		unsigned long pfn = mfn_to_pfn(mfn);
-
 		pteval_t flags = val & PTE_FLAGS_MASK;
-		if (unlikely(pfn == ~0))
-			val = flags & ~_PAGE_PRESENT;
-		else
+
+		if (likely(pfn != ~0))
 			val = ((pteval_t)pfn << PAGE_SHIFT) | flags;
 	}
 
@@ -390,6 +388,7 @@ static pteval_t pte_pfn_to_mfn(pteval_t val)
 			mfn = get_phys_to_machine(pfn);
 		else
 			mfn = pfn;
+
 		/*
 		 * If there's no mfn for the pfn, then just create an
 		 * empty non-present pte.  Unfortunately this loses
@@ -399,38 +398,15 @@ static pteval_t pte_pfn_to_mfn(pteval_t val)
 		if (unlikely(mfn == INVALID_P2M_ENTRY)) {
 			mfn = 0;
 			flags = 0;
-		} else {
-			/*
-			 * Paramount to do this test _after_ the
-			 * INVALID_P2M_ENTRY as INVALID_P2M_ENTRY &
-			 * IDENTITY_FRAME_BIT resolves to true.
-			 */
-			mfn &= ~FOREIGN_FRAME_BIT;
-			if (mfn & IDENTITY_FRAME_BIT) {
-				mfn &= ~IDENTITY_FRAME_BIT;
-				flags |= _PAGE_IOMAP;
-			}
-		}
+			mfn = pfn;
+		} else
+			mfn &= ~(FOREIGN_FRAME_BIT | IDENTITY_FRAME_BIT);
 		val = ((pteval_t)mfn << PAGE_SHIFT) | flags;
 	}
 
 	return val;
 }
 
-static pteval_t iomap_pte(pteval_t val)
-{
-	if (val & _PAGE_PRESENT) {
-		unsigned long pfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
-		pteval_t flags = val & PTE_FLAGS_MASK;
-
-		/* We assume the pte frame number is a MFN, so
-		   just use it as-is. */
-		val = ((pteval_t)pfn << PAGE_SHIFT) | flags;
-	}
-
-	return val;
-}
-
 static pteval_t xen_pte_val(pte_t pte)
 {
 	pteval_t pteval = pte.pte;
@@ -441,9 +417,6 @@ static pteval_t xen_pte_val(pte_t pte)
 		pteval = (pteval & ~_PAGE_PAT) | _PAGE_PWT;
 	}
 #endif
-	if (xen_initial_domain() && (pteval & _PAGE_IOMAP))
-		return pteval;
-
 	return pte_mfn_to_pfn(pteval);
 }
 PV_CALLEE_SAVE_REGS_THUNK(xen_pte_val);
@@ -481,7 +454,6 @@ void xen_set_pat(u64 pat)
 
 static pte_t xen_make_pte(pteval_t pte)
 {
-	phys_addr_t addr = (pte & PTE_PFN_MASK);
 #if 0
 	/* If Linux is trying to set a WC pte, then map to the Xen WC.
 	 * If _PAGE_PAT is set, then it probably means it is really
@@ -496,19 +468,7 @@ static pte_t xen_make_pte(pteval_t pte)
 			pte = (pte & ~(_PAGE_PCD | _PAGE_PWT)) | _PAGE_PAT;
 	}
 #endif
-	/*
-	 * Unprivileged domains are allowed to do IOMAPpings for
-	 * PCI passthrough, but not map ISA space.  The ISA
-	 * mappings are just dummy local mappings to keep other
-	 * parts of the kernel happy.
-	 */
-	if (unlikely(pte & _PAGE_IOMAP) &&
-	    (xen_initial_domain() || addr >= ISA_END_ADDRESS)) {
-		pte = iomap_pte(pte);
-	} else {
-		pte &= ~_PAGE_IOMAP;
-		pte = pte_pfn_to_mfn(pte);
-	}
+	pte = pte_pfn_to_mfn(pte);
 
 	return native_make_pte(pte);
 }
@@ -2084,7 +2044,7 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
 
 	default:
 		/* By default, set_fixmap is used for hardware mappings */
-		pte = mfn_pte(phys, __pgprot(pgprot_val(prot) | _PAGE_IOMAP));
+		pte = mfn_pte(phys, prot);
 		break;
 	}
 
@@ -2524,8 +2484,6 @@ int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
 	if (xen_feature(XENFEAT_auto_translated_physmap))
 		return -EINVAL;
 
-	prot = __pgprot(pgprot_val(prot) | _PAGE_IOMAP);
-
 	BUG_ON(!((vma->vm_flags & (VM_PFNMAP | VM_IO)) == (VM_PFNMAP | VM_IO)));
 
 	rmd.mfn = mfn;
-- 
1.7.2.5

Re: [PATCH 1/2] x86/xen: set regions above the end of RAM as 1:1

[Stefano Stabellini]

On Fri, 3 Jan 2014, David Vrabel wrote:
> From: David Vrabel <david.vrabel@citrix.com>
> 
> PCI devices may have BARs located above the end of RAM so mark such
> frames as identity frames in the p2m (instead of the default of
> missing).
> 
> PFNs outside the p2m (above MAX_P2M_PFN) are also considered to be
> identity frames for the same reason.
> 
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>

Shouldn't this be the case only for dom0?


>  arch/x86/xen/p2m.c   |    2 +-
>  arch/x86/xen/setup.c |   10 ++++++++++
>  2 files changed, 11 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> index 2ae8699..a905355 100644
> --- a/arch/x86/xen/p2m.c
> +++ b/arch/x86/xen/p2m.c
> @@ -481,7 +481,7 @@ unsigned long get_phys_to_machine(unsigned long pfn)
>  	unsigned topidx, mididx, idx;
>  
>  	if (unlikely(pfn >= MAX_P2M_PFN))
> -		return INVALID_P2M_ENTRY;
> +		return IDENTITY_FRAME(pfn);
>  
>  	topidx = p2m_top_index(pfn);
>  	mididx = p2m_mid_index(pfn);
> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> index 68c054f..6d7798f 100644
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -412,6 +412,16 @@ char * __init xen_memory_setup(void)
>  		max_pfn = min(MAX_DOMAIN_PAGES, last_pfn);
>  		mem_end = PFN_PHYS(max_pfn);
>  	}
> +
> +	/*
> +	 * Set the rest as identity mapped, in case PCI BARs are
> +	 * located here.
> +	 *
> +	 * PFNs above MAX_P2M_PFN are considered identity mapped as
> +	 * well.
> +	 */
> +	set_phys_range_identity(max_pfn + 1, ~0ul);
> +

Wouldn't this increase the size of the P2M considerably?


>  	 * Clamp the amount of extra memory to a EXTRA_MEM_RATIO
>  	 * factor the base size.  On non-highmem systems, the base
> -- 
> 1.7.2.5
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
> 

Re: [PATCH 2/2] x86/xen: make mfn_to_pfn() work with MFNs that are 1:1 in the p2m

[Stefano Stabellini]

On Fri, 3 Jan 2014, David Vrabel wrote:
> From: David Vrabel <david.vrabel@citrix.com>
> 
> The _PAGE_IOMAP PTE flag is used to indicate that the PTE contains an
> MFN that is an identify frame (1:1) in the p2m.  This is so the
> correct conversion of MFN to PFN can be done reading a PTE.
> 
> If mfn_to_pfn() returned the correct PFN instead the _PAGE_IOMAP flag
> is not required and can be removed.
> 
> In mfn_to_pfn() the PFN found in the M2P is checked in P2M.  If the
> two MFNs differ then the MFN is one of three possibilities:
> 
>   a) its a foreign MFN with an m2p override.
> 
>   b) it's a foreign MFN with /no/ m2p override.
> 
>   c) it's a identity MFN.
> 
> It is not permitted to call mfn_to_pfn() no a foreign MFN without an
> override was the resulting PFN will not incorrect.  We can therefore
> assume case (c) and return PFN == MFN.
> 
> [ This patch should probably be split into the Xen-specific parts and
> an x86 patch to remove _PAGE_IOMAP. ]
> 
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> ---
>  arch/x86/include/asm/pgtable_types.h |   12 +++---
>  arch/x86/include/asm/xen/page.h      |   18 +++++++---
>  arch/x86/mm/init_32.c                |    2 +-
>  arch/x86/mm/init_64.c                |    2 +-
>  arch/x86/pci/i386.c                  |    2 -
>  arch/x86/xen/enlighten.c             |    2 -
>  arch/x86/xen/mmu.c                   |   58 +++++-----------------------------
>  7 files changed, 28 insertions(+), 68 deletions(-)
> 
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> index 0ecac25..0b12657 100644
> diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
> index b913915..eb11963 100644
> --- a/arch/x86/include/asm/xen/page.h
> +++ b/arch/x86/include/asm/xen/page.h
> @@ -112,11 +112,18 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
>  	pfn = mfn_to_pfn_no_overrides(mfn);
>  	if (get_phys_to_machine(pfn) != mfn) {
>  		/*
> -		 * If this appears to be a foreign mfn (because the pfn
> -		 * doesn't map back to the mfn), then check the local override
> -		 * table to see if there's a better pfn to use.
> +		 * This is either:
>  		 *
> -		 * m2p_find_override_pfn returns ~0 if it doesn't find anything.
> +		 * a) a foreign MFN with an override.
> +		 *
> +		 * b) a foreign MFN without an override.
> +		 *
> +		 * c) an identity MFN that is not in the the p2m.

You have missed a case here:

           d) a local MFN with an override

think of blkfront and blkback in the same domain.
However I don't think this case would be affected by the patch.


> +		 * For (a), look in the m2p overrides.  For (b) and
> +		 * (c) assume identify MFN since mfn_to_pfn() will
> +		 * only be called on foreign MFNs iff they have
> +		 * overrides.
>  		 */
>  		pfn = m2p_find_override_pfn(mfn, ~0);
>  	}
> @@ -126,8 +133,7 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
>  	 * entry doesn't map back to the mfn and m2p_override doesn't have a
>  	 * valid entry for it.
>  	 */
> -	if (pfn == ~0 &&
> -			get_phys_to_machine(mfn) == IDENTITY_FRAME(mfn))
> +	if (pfn == ~0)
>  		pfn = mfn;
>  
>  	return pfn;

Re: [PATCH 2/2] x86/xen: make mfn_to_pfn() work with MFNs that are 1:1 in the p2m

[Konrad Rzeszutek Wilk]

On Fri, Jan 03, 2014 at 04:45:22PM +0000, David Vrabel wrote:
> From: David Vrabel <david.vrabel@citrix.com>
> 
> The _PAGE_IOMAP PTE flag is used to indicate that the PTE contains an
> MFN that is an identify frame (1:1) in the p2m.  This is so the
> correct conversion of MFN to PFN can be done reading a PTE.
> 
> If mfn_to_pfn() returned the correct PFN instead the _PAGE_IOMAP flag
> is not required and can be removed.
> 
> In mfn_to_pfn() the PFN found in the M2P is checked in P2M.  If the
> two MFNs differ then the MFN is one of three possibilities:
> 
>   a) its a foreign MFN with an m2p override.
> 
>   b) it's a foreign MFN with /no/ m2p override.
> 
>   c) it's a identity MFN.
> 
> It is not permitted to call mfn_to_pfn() no a foreign MFN without an
> override was the resulting PFN will not incorrect.  We can therefore
> assume case (c) and return PFN == MFN.
> 
> [ This patch should probably be split into the Xen-specific parts and
> an x86 patch to remove _PAGE_IOMAP. ]

Yeah :-)

> 
> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> ---
>  arch/x86/include/asm/pgtable_types.h |   12 +++---
>  arch/x86/include/asm/xen/page.h      |   18 +++++++---
>  arch/x86/mm/init_32.c                |    2 +-
>  arch/x86/mm/init_64.c                |    2 +-
>  arch/x86/pci/i386.c                  |    2 -
>  arch/x86/xen/enlighten.c             |    2 -
>  arch/x86/xen/mmu.c                   |   58 +++++-----------------------------
>  7 files changed, 28 insertions(+), 68 deletions(-)
> 
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> index 0ecac25..0b12657 100644
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -17,7 +17,7 @@
>  #define _PAGE_BIT_PAT		7	/* on 4KB pages */
>  #define _PAGE_BIT_GLOBAL	8	/* Global TLB entry PPro+ */
>  #define _PAGE_BIT_UNUSED1	9	/* available for programmer */
> -#define _PAGE_BIT_IOMAP		10	/* flag used to indicate IO mapping */
> +#define _PAGE_BIT_UNUSED2	10	/* available for programmer */
>  #define _PAGE_BIT_HIDDEN	11	/* hidden by kmemcheck */
>  #define _PAGE_BIT_PAT_LARGE	12	/* On 2MB or 1GB pages */
>  #define _PAGE_BIT_SPECIAL	_PAGE_BIT_UNUSED1
> @@ -41,7 +41,7 @@
>  #define _PAGE_PSE	(_AT(pteval_t, 1) << _PAGE_BIT_PSE)
>  #define _PAGE_GLOBAL	(_AT(pteval_t, 1) << _PAGE_BIT_GLOBAL)
>  #define _PAGE_UNUSED1	(_AT(pteval_t, 1) << _PAGE_BIT_UNUSED1)
> -#define _PAGE_IOMAP	(_AT(pteval_t, 1) << _PAGE_BIT_IOMAP)
> +#define _PAGE_UNUSED2	(_AT(pteval_t, 1) << _PAGE_BIT_UNUSED2)
>  #define _PAGE_PAT	(_AT(pteval_t, 1) << _PAGE_BIT_PAT)
>  #define _PAGE_PAT_LARGE (_AT(pteval_t, 1) << _PAGE_BIT_PAT_LARGE)
>  #define _PAGE_SPECIAL	(_AT(pteval_t, 1) << _PAGE_BIT_SPECIAL)
> @@ -163,10 +163,10 @@
>  #define __PAGE_KERNEL_LARGE_NOCACHE	(__PAGE_KERNEL | _PAGE_CACHE_UC | _PAGE_PSE)
>  #define __PAGE_KERNEL_LARGE_EXEC	(__PAGE_KERNEL_EXEC | _PAGE_PSE)
>  
> -#define __PAGE_KERNEL_IO		(__PAGE_KERNEL | _PAGE_IOMAP)
> -#define __PAGE_KERNEL_IO_NOCACHE	(__PAGE_KERNEL_NOCACHE | _PAGE_IOMAP)
> -#define __PAGE_KERNEL_IO_UC_MINUS	(__PAGE_KERNEL_UC_MINUS | _PAGE_IOMAP)
> -#define __PAGE_KERNEL_IO_WC		(__PAGE_KERNEL_WC | _PAGE_IOMAP)
> +#define __PAGE_KERNEL_IO		(__PAGE_KERNEL)
> +#define __PAGE_KERNEL_IO_NOCACHE	(__PAGE_KERNEL_NOCACHE)
> +#define __PAGE_KERNEL_IO_UC_MINUS	(__PAGE_KERNEL_UC_MINUS)
> +#define __PAGE_KERNEL_IO_WC		(__PAGE_KERNEL_WC)
>  
>  #define PAGE_KERNEL			__pgprot(__PAGE_KERNEL)
>  #define PAGE_KERNEL_RO			__pgprot(__PAGE_KERNEL_RO)
> diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
> index b913915..eb11963 100644
> --- a/arch/x86/include/asm/xen/page.h
> +++ b/arch/x86/include/asm/xen/page.h
> @@ -112,11 +112,18 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
>  	pfn = mfn_to_pfn_no_overrides(mfn);
>  	if (get_phys_to_machine(pfn) != mfn) {
>  		/*
> -		 * If this appears to be a foreign mfn (because the pfn
> -		 * doesn't map back to the mfn), then check the local override
> -		 * table to see if there's a better pfn to use.
> +		 * This is either:
>  		 *
> -		 * m2p_find_override_pfn returns ~0 if it doesn't find anything.
> +		 * a) a foreign MFN with an override.
> +		 *
> +		 * b) a foreign MFN without an override.
> +		 *
> +		 * c) an identity MFN that is not in the the p2m.
> +		 *
> +		 * For (a), look in the m2p overrides.  For (b) and
> +		 * (c) assume identify MFN since mfn_to_pfn() will
> +		 * only be called on foreign MFNs iff they have
> +		 * overrides.
>  		 */
>  		pfn = m2p_find_override_pfn(mfn, ~0);
>  	}
> @@ -126,8 +133,7 @@ static inline unsigned long mfn_to_pfn(unsigned long mfn)
>  	 * entry doesn't map back to the mfn and m2p_override doesn't have a
>  	 * valid entry for it.
>  	 */
> -	if (pfn == ~0 &&
> -			get_phys_to_machine(mfn) == IDENTITY_FRAME(mfn))
> +	if (pfn == ~0)
>  		pfn = mfn;
>  
>  	return pfn;
> diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
> index 4287f1f..9031593 100644
> --- a/arch/x86/mm/init_32.c
> +++ b/arch/x86/mm/init_32.c
> @@ -537,7 +537,7 @@ static void __init pagetable_init(void)
>  	permanent_kmaps_init(pgd_base);
>  }
>  
> -pteval_t __supported_pte_mask __read_mostly = ~(_PAGE_NX | _PAGE_GLOBAL | _PAGE_IOMAP);
> +pteval_t __supported_pte_mask __read_mostly = ~(_PAGE_NX | _PAGE_GLOBAL);
>  EXPORT_SYMBOL_GPL(__supported_pte_mask);
>  
>  /* user-defined highmem size */
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 104d56a..68bf948 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -151,7 +151,7 @@ early_param("gbpages", parse_direct_gbpages_on);
>   * around without checking the pgd every time.
>   */
>  
> -pteval_t __supported_pte_mask __read_mostly = ~_PAGE_IOMAP;
> +pteval_t __supported_pte_mask __read_mostly = ~0;
>  EXPORT_SYMBOL_GPL(__supported_pte_mask);
>  
>  int force_personality32;
> diff --git a/arch/x86/pci/i386.c b/arch/x86/pci/i386.c
> index db6b1ab..1f642d6 100644
> --- a/arch/x86/pci/i386.c
> +++ b/arch/x86/pci/i386.c
> @@ -433,8 +433,6 @@ int pci_mmap_page_range(struct pci_dev *dev, struct vm_area_struct *vma,
>  		 */
>  		prot |= _PAGE_CACHE_UC_MINUS;
>  
> -	prot |= _PAGE_IOMAP;	/* creating a mapping for IO */
> -
>  	vma->vm_page_prot = __pgprot(prot);
>  
>  	if (io_remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff,
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index fa6ade7..f9c2d71 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -1458,8 +1458,6 @@ asmlinkage void __init xen_start_kernel(void)
>  #endif
>  		__supported_pte_mask &= ~(_PAGE_PWT | _PAGE_PCD);
>  
> -	__supported_pte_mask |= _PAGE_IOMAP;
> -
>  	/*
>  	 * Prevent page tables from being allocated in highmem, even
>  	 * if CONFIG_HIGHPTE is enabled.
> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
> index ce563be..5fa77a1 100644
> --- a/arch/x86/xen/mmu.c
> +++ b/arch/x86/xen/mmu.c
> @@ -368,11 +368,9 @@ static pteval_t pte_mfn_to_pfn(pteval_t val)
>  	if (val & _PAGE_PRESENT) {
>  		unsigned long mfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
>  		unsigned long pfn = mfn_to_pfn(mfn);
> -
>  		pteval_t flags = val & PTE_FLAGS_MASK;
> -		if (unlikely(pfn == ~0))
> -			val = flags & ~_PAGE_PRESENT;
> -		else
> +
> +		if (likely(pfn != ~0))
>  			val = ((pteval_t)pfn << PAGE_SHIFT) | flags;
>  	}
>  
> @@ -390,6 +388,7 @@ static pteval_t pte_pfn_to_mfn(pteval_t val)
>  			mfn = get_phys_to_machine(pfn);
>  		else
>  			mfn = pfn;
> +
>  		/*
>  		 * If there's no mfn for the pfn, then just create an
>  		 * empty non-present pte.  Unfortunately this loses
> @@ -399,38 +398,15 @@ static pteval_t pte_pfn_to_mfn(pteval_t val)
>  		if (unlikely(mfn == INVALID_P2M_ENTRY)) {
>  			mfn = 0;
>  			flags = 0;
> -		} else {
> -			/*
> -			 * Paramount to do this test _after_ the
> -			 * INVALID_P2M_ENTRY as INVALID_P2M_ENTRY &
> -			 * IDENTITY_FRAME_BIT resolves to true.
> -			 */
> -			mfn &= ~FOREIGN_FRAME_BIT;
> -			if (mfn & IDENTITY_FRAME_BIT) {
> -				mfn &= ~IDENTITY_FRAME_BIT;
> -				flags |= _PAGE_IOMAP;
> -			}
> -		}
> +			mfn = pfn;
> +		} else
> +			mfn &= ~(FOREIGN_FRAME_BIT | IDENTITY_FRAME_BIT);
>  		val = ((pteval_t)mfn << PAGE_SHIFT) | flags;
>  	}
>  
>  	return val;
>  }
>  
> -static pteval_t iomap_pte(pteval_t val)
> -{
> -	if (val & _PAGE_PRESENT) {
> -		unsigned long pfn = (val & PTE_PFN_MASK) >> PAGE_SHIFT;
> -		pteval_t flags = val & PTE_FLAGS_MASK;
> -
> -		/* We assume the pte frame number is a MFN, so
> -		   just use it as-is. */
> -		val = ((pteval_t)pfn << PAGE_SHIFT) | flags;
> -	}
> -
> -	return val;
> -}
> -
>  static pteval_t xen_pte_val(pte_t pte)
>  {
>  	pteval_t pteval = pte.pte;
> @@ -441,9 +417,6 @@ static pteval_t xen_pte_val(pte_t pte)
>  		pteval = (pteval & ~_PAGE_PAT) | _PAGE_PWT;
>  	}
>  #endif
> -	if (xen_initial_domain() && (pteval & _PAGE_IOMAP))
> -		return pteval;
> -
>  	return pte_mfn_to_pfn(pteval);
>  }
>  PV_CALLEE_SAVE_REGS_THUNK(xen_pte_val);
> @@ -481,7 +454,6 @@ void xen_set_pat(u64 pat)
>  
>  static pte_t xen_make_pte(pteval_t pte)
>  {
> -	phys_addr_t addr = (pte & PTE_PFN_MASK);
>  #if 0
>  	/* If Linux is trying to set a WC pte, then map to the Xen WC.
>  	 * If _PAGE_PAT is set, then it probably means it is really
> @@ -496,19 +468,7 @@ static pte_t xen_make_pte(pteval_t pte)
>  			pte = (pte & ~(_PAGE_PCD | _PAGE_PWT)) | _PAGE_PAT;
>  	}
>  #endif
> -	/*
> -	 * Unprivileged domains are allowed to do IOMAPpings for
> -	 * PCI passthrough, but not map ISA space.  The ISA
> -	 * mappings are just dummy local mappings to keep other
> -	 * parts of the kernel happy.
> -	 */
> -	if (unlikely(pte & _PAGE_IOMAP) &&
> -	    (xen_initial_domain() || addr >= ISA_END_ADDRESS)) {
> -		pte = iomap_pte(pte);
> -	} else {
> -		pte &= ~_PAGE_IOMAP;
> -		pte = pte_pfn_to_mfn(pte);
> -	}
> +	pte = pte_pfn_to_mfn(pte);
>  
>  	return native_make_pte(pte);
>  }
> @@ -2084,7 +2044,7 @@ static void xen_set_fixmap(unsigned idx, phys_addr_t phys, pgprot_t prot)
>  
>  	default:
>  		/* By default, set_fixmap is used for hardware mappings */
> -		pte = mfn_pte(phys, __pgprot(pgprot_val(prot) | _PAGE_IOMAP));
> +		pte = mfn_pte(phys, prot);
>  		break;
>  	}
>  
> @@ -2524,8 +2484,6 @@ int xen_remap_domain_mfn_range(struct vm_area_struct *vma,
>  	if (xen_feature(XENFEAT_auto_translated_physmap))
>  		return -EINVAL;
>  
> -	prot = __pgprot(pgprot_val(prot) | _PAGE_IOMAP);
> -
>  	BUG_ON(!((vma->vm_flags & (VM_PFNMAP | VM_IO)) == (VM_PFNMAP | VM_IO)));
>  
>  	rmd.mfn = mfn;
> -- 
> 1.7.2.5
> 

Re: [PATCH 1/2] x86/xen: set regions above the end of RAM as 1:1

[Konrad Rzeszutek Wilk]

On Fri, Jan 03, 2014 at 06:12:26PM +0000, Stefano Stabellini wrote:
> On Fri, 3 Jan 2014, David Vrabel wrote:
> > From: David Vrabel <david.vrabel@citrix.com>
> > 
> > PCI devices may have BARs located above the end of RAM so mark such
> > frames as identity frames in the p2m (instead of the default of
> > missing).
> > 
> > PFNs outside the p2m (above MAX_P2M_PFN) are also considered to be
> > identity frames for the same reason.
> > 
> > Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> 
> Shouldn't this be the case only for dom0?

You can have PV guests with PCI passthrough that depend on identity
MFNs.

Which is interesting - because if we do not have the E820 setup
to reflect the memory correct (and especially the MMIO regions), we
are screwed. Unless the user boots this PV guest with memory right
up to the MMIO BAR.

The 'e820_hole=1' parameter helps in fabricating an E820 for PV
guests that looks like the hosts - with the nice mix of E820_RSV
and MMIO bars.

> 
> 
> >  arch/x86/xen/p2m.c   |    2 +-
> >  arch/x86/xen/setup.c |   10 ++++++++++
> >  2 files changed, 11 insertions(+), 1 deletions(-)
> > 
> > diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> > index 2ae8699..a905355 100644
> > --- a/arch/x86/xen/p2m.c
> > +++ b/arch/x86/xen/p2m.c
> > @@ -481,7 +481,7 @@ unsigned long get_phys_to_machine(unsigned long pfn)
> >  	unsigned topidx, mididx, idx;
> >  
> >  	if (unlikely(pfn >= MAX_P2M_PFN))
> > -		return INVALID_P2M_ENTRY;
> > +		return IDENTITY_FRAME(pfn);
> >  
> >  	topidx = p2m_top_index(pfn);
> >  	mididx = p2m_mid_index(pfn);
> > diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> > index 68c054f..6d7798f 100644
> > --- a/arch/x86/xen/setup.c
> > +++ b/arch/x86/xen/setup.c
> > @@ -412,6 +412,16 @@ char * __init xen_memory_setup(void)
> >  		max_pfn = min(MAX_DOMAIN_PAGES, last_pfn);
> >  		mem_end = PFN_PHYS(max_pfn);
> >  	}
> > +
> > +	/*
> > +	 * Set the rest as identity mapped, in case PCI BARs are
> > +	 * located here.
> > +	 *
> > +	 * PFNs above MAX_P2M_PFN are considered identity mapped as
> > +	 * well.
> > +	 */
> > +	set_phys_range_identity(max_pfn + 1, ~0ul);
> > +
> 
> Wouldn't this increase the size of the P2M considerably?

Yes. The P2M[4->500] parts will end up being allocated (if you
boot with a 4GB guest/dom0). One thought I had was to have a
p2m_top_missing to be a 'P2M' 'identity' type so you don't waste
that much memory. Similary to how the checks are done against
'p2m_missing' right now.


The neat thing with this patch is that regions _after_ the P2M
(so past the 500GB) are solved with this patch. 
(which is what the original bug was about).
> 
> 
> >  	 * Clamp the amount of extra memory to a EXTRA_MEM_RATIO
> >  	 * factor the base size.  On non-highmem systems, the base
> > -- 
> > 1.7.2.5
> > 
> > 
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.xen.org
> > http://lists.xen.org/xen-devel
> > 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel

Re: [PATCH RFC 0/2] Linux: possible ixes for mapping high MMIO regions

[Konrad Rzeszutek Wilk]

On Fri, Jan 03, 2014 at 04:45:20PM +0000, David Vrabel wrote:
> This a possible fix for the problems with mapping high MMIO regions in
> certain cases (e.g., the RDMA drivers) as not all mappers were
> specifing the _PAGE_IOMAP which meant no valid MFN could be found and
> the resulting PTE would be marked as not present, causing subsequent
> faults.
> 
> It assumes that anything that isn't RAM (whether ballooned out or not)
> is an I/O region and thus should be 1:1 in the p2m.  Ballooned frames
> are still marked as missing in the p2m as before.
> 
> As a follow on, mfn_to_pfn() is (hopefully) extended to do the right
> thing with such an MFN.  This means the Xen-specific _PAGE_IOMAP PTE
> flag can be removed,

Woot!
> 
> This series is posted as an early RFC in the hope that is an
> acceptable approach.  It has only seen the bare minimum of smoke
> testing (my test dom0 didn't explode). In particular, I've not
> actually tested it with a device with a high MMIO.

I can do in a couple of weeks.
> 
> David
> 

Re: [PATCH 1/2] x86/xen: set regions above the end of RAM as 1:1

[David Vrabel]

On 03/01/14 18:12, Stefano Stabellini wrote:
> On Fri, 3 Jan 2014, David Vrabel wrote:
>> From: David Vrabel <david.vrabel@citrix.com>
>>
>> PCI devices may have BARs located above the end of RAM so mark such
>> frames as identity frames in the p2m (instead of the default of
>> missing).
>>
>> PFNs outside the p2m (above MAX_P2M_PFN) are also considered to be
>> identity frames for the same reason.
>>
>> Signed-off-by: David Vrabel <david.vrabel@citrix.com>
> 
> Shouldn't this be the case only for dom0?

I don't see why.  DomUs can have PCI devices with high MMIO regions
passed-through.

>> --- a/arch/x86/xen/p2m.c
>> +++ b/arch/x86/xen/p2m.c
>> @@ -481,7 +481,7 @@ unsigned long get_phys_to_machine(unsigned long pfn)
>>  	unsigned topidx, mididx, idx;
>>  
>>  	if (unlikely(pfn >= MAX_P2M_PFN))
>> -		return INVALID_P2M_ENTRY;
>> +		return IDENTITY_FRAME(pfn);
>>  
>>  	topidx = p2m_top_index(pfn);
>>  	mididx = p2m_mid_index(pfn);
>> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
>> index 68c054f..6d7798f 100644
>> --- a/arch/x86/xen/setup.c
>> +++ b/arch/x86/xen/setup.c
>> @@ -412,6 +412,16 @@ char * __init xen_memory_setup(void)
>>  		max_pfn = min(MAX_DOMAIN_PAGES, last_pfn);
>>  		mem_end = PFN_PHYS(max_pfn);
>>  	}
>> +
>> +	/*
>> +	 * Set the rest as identity mapped, in case PCI BARs are
>> +	 * located here.
>> +	 *
>> +	 * PFNs above MAX_P2M_PFN are considered identity mapped as
>> +	 * well.
>> +	 */
>> +	set_phys_range_identity(max_pfn + 1, ~0ul);
>> +
> 
> Wouldn't this increase the size of the P2M considerably?

I thought the p2m code would be smart but I see I need to add a
p2m_mid_identity page (similar to the existign p2m_mid_missing page) and
make sure we use it.

David