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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

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
>