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Re: [Xen-devel] x86-64 machine_to_phys vs NX bit

To: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>

From: John Byrne <john.l.byrne@xxxxxx>

Date: Mon, 13 Nov 2006 17:15:16 -0800

Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxxxx>

Delivery-date: Mon, 13 Nov 2006 17:15:50 -0800

List-id: Xen developer discussion <xen-devel.lists.xensource.com>

John Byrne wrote:

Keir Fraser wrote:

On 13/11/06 8:07 am, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
There was a bug in my previous patch. (There's nothing like trying to
get to sleep and realizing you've screwed up.) The x86 pae
PHYSICAL_PAGE_MASK I defined was incorrect because PAGE_MASK was only a
long. I hope I haven't done anything else wrong.
I don't think this is correct - machine_to_phys() translates amachine addressto a physical one, and in that translation the upper bits matter onlyas muchas mfn_to_pfn() should return an invalid indicator if any of them isset. In
turn,
it should be the caller's responsibility to make sure the NX bit (andany
potential
other one being set beyond bit 52) gets masked off *before* calling this
function. (Specifically, the preserving of the lower bits is to properly
translate
a non-page aligned address, not to preserve attribute bits read froma page
table entry).
Yes, we should keep the old machine_to_phys() definition and renameJohn's
new version as pte_machine_to_phys(). The latter should be used in all
contexts where machine_to_phys() currently operates on a pte (that'smost ofits uses, actually). This is a worthwhile cleanup and clarification.Could
you respin the patch, John?

 Thanks,
 Keir


I've  made the change. I'll send it out after I've built and tested it.

John

Here's the new patch. Signed-off-by: John Byrne <john.l.byrne@xxxxxx>

diff -r d19deb173503 linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/maddr.h --- a/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/maddr.h Fri Nov 10 15:27:22 2006 +0000 +++ b/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/maddr.h Mon Nov 13 14:32:15 2006 -0600 @@ -127,10 +127,24 @@ static inline maddr_t phys_to_machine(pa machine = (machine << PAGE_SHIFT) | (phys & ~PAGE_MASK); return machine; } + static inline paddr_t machine_to_phys(maddr_t machine) { paddr_t phys = mfn_to_pfn(machine >> PAGE_SHIFT); phys = (phys << PAGE_SHIFT) | (machine & ~PAGE_MASK); + return phys; +} + +static inline paddr_t pte_machine_to_phys(maddr_t machine) +{ + /* + * In PAE mode, the NX bit needs to be dealt with in the value + * passed to mfn_to_pfn(). On x86_64, we need to mask it off, + * but for i386 the conversion to ulong for the argument will + * clip it off. + */ + paddr_t phys = mfn_to_pfn(machine >> PAGE_SHIFT); + phys = (phys << PAGE_SHIFT) | (machine & ~PHYSICAL_PAGE_MASK); return phys; } diff -r d19deb173503 linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/page.h --- a/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/page.h Fri Nov 10 15:27:22 2006 +0000 +++ b/linux-2.6-xen-sparse/include/asm-i386/mach-xen/asm/page.h Mon Nov 13 14:31:16 2006 -0600 @@ -5,6 +5,16 @@ #define PAGE_SHIFT 12 #define PAGE_SIZE (1UL << PAGE_SHIFT) #define PAGE_MASK (~(PAGE_SIZE-1)) + +#ifdef CONFIG_X86_PAE +#define __PHYSICAL_MASK_SHIFT 36 +#define __PHYSICAL_MASK ((1ULL << __PHYSICAL_MASK_SHIFT) - 1) +#define PHYSICAL_PAGE_MASK (~((1ULL << PAGE_SHIFT) - 1) & __PHYSICAL_MASK) +#else +#define __PHYSICAL_MASK_SHIFT 32 +#define __PHYSICAL_MASK (~0UL) +#define PHYSICAL_PAGE_MASK (PAGE_MASK & __PHYSICAL_MASK) +#endif #define LARGE_PAGE_MASK (~(LARGE_PAGE_SIZE-1)) #define LARGE_PAGE_SIZE (1UL << PMD_SHIFT) @@ -85,7 +95,7 @@ static inline unsigned long long pte_val if (x.pte_low) { ret = x.pte_low | (unsigned long long)x.pte_high << 32; - ret = machine_to_phys(ret) | 1; + ret = pte_machine_to_phys(ret) | 1; } else { ret = 0; } @@ -94,13 +104,13 @@ static inline unsigned long long pmd_val static inline unsigned long long pmd_val(pmd_t x) { unsigned long long ret = x.pmd; - if (ret) ret = machine_to_phys(ret) | 1; + if (ret) ret = pte_machine_to_phys(ret) | 1; return ret; } static inline unsigned long long pgd_val(pgd_t x) { unsigned long long ret = x.pgd; - if (ret) ret = machine_to_phys(ret) | 1; + if (ret) ret = pte_machine_to_phys(ret) | 1; return ret; } static inline unsigned long long pte_val_ma(pte_t x) @@ -115,7 +125,8 @@ typedef struct { unsigned long pgprot; } #define pgprot_val(x) ((x).pgprot) #include <asm/maddr.h> #define boot_pte_t pte_t /* or would you rather have a typedef */ -#define pte_val(x) (((x).pte_low & 1) ? machine_to_phys((x).pte_low) : \ +#define pte_val(x) (((x).pte_low & 1) ? \ + pte_machine_to_phys((x).pte_low) : \ (x).pte_low) #define pte_val_ma(x) ((x).pte_low) #define __pte(x) ({ unsigned long _x = (x); \ @@ -125,7 +136,7 @@ static inline unsigned long pgd_val(pgd_ static inline unsigned long pgd_val(pgd_t x) { unsigned long ret = x.pgd; - if (ret) ret = machine_to_phys(ret) | 1; + if (ret) ret = pte_machine_to_phys(ret) | 1; return ret; } #define HPAGE_SHIFT 22 diff -r d19deb173503 linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/maddr.h --- a/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/maddr.h Fri Nov 10 15:27:22 2006 +0000 +++ b/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/maddr.h Mon Nov 13 14:35:30 2006 -0600 @@ -127,6 +127,14 @@ static inline paddr_t machine_to_phys(ma return phys; } +static inline paddr_t pte_machine_to_phys(maddr_t machine) +{ + paddr_t phys; + phys = mfn_to_pfn((machine & PHYSICAL_PAGE_MASK) >> PAGE_SHIFT); + phys = (phys << PAGE_SHIFT) | (machine & ~PHYSICAL_PAGE_MASK); + return phys; +} + /* VIRT <-> MACHINE conversion */ #define virt_to_machine(v) (phys_to_machine(__pa(v))) #define virt_to_mfn(v) (pfn_to_mfn(__pa(v) >> PAGE_SHIFT)) diff -r d19deb173503 linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/page.h --- a/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/page.h Fri Nov 10 15:27:22 2006 +0000 +++ b/linux-2.6-xen-sparse/include/asm-x86_64/mach-xen/asm/page.h Mon Nov 13 14:33:02 2006 -0600 @@ -33,6 +33,13 @@ #define PAGE_SIZE (1UL << PAGE_SHIFT) #endif #define PAGE_MASK (~(PAGE_SIZE-1)) + +/* See Documentation/x86_64/mm.txt for a description of the memory map. */ +#define __PHYSICAL_MASK_SHIFT 46 +#define __PHYSICAL_MASK ((1UL << __PHYSICAL_MASK_SHIFT) - 1) +#define __VIRTUAL_MASK_SHIFT 48 +#define __VIRTUAL_MASK ((1UL << __VIRTUAL_MASK_SHIFT) - 1) + #define PHYSICAL_PAGE_MASK (~(PAGE_SIZE-1) & __PHYSICAL_MASK) #define THREAD_ORDER 1 @@ -90,28 +97,28 @@ typedef struct { unsigned long pgd; } pg typedef struct { unsigned long pgprot; } pgprot_t; -#define pte_val(x) (((x).pte & 1) ? machine_to_phys((x).pte) : \ +#define pte_val(x) (((x).pte & 1) ? pte_machine_to_phys((x).pte) : \ (x).pte) #define pte_val_ma(x) ((x).pte) static inline unsigned long pmd_val(pmd_t x) { unsigned long ret = x.pmd; - if (ret) ret = machine_to_phys(ret); + if (ret) ret = pte_machine_to_phys(ret); return ret; } static inline unsigned long pud_val(pud_t x) { unsigned long ret = x.pud; - if (ret) ret = machine_to_phys(ret); + if (ret) ret = pte_machine_to_phys(ret); return ret; } static inline unsigned long pgd_val(pgd_t x) { unsigned long ret = x.pgd; - if (ret) ret = machine_to_phys(ret); + if (ret) ret = pte_machine_to_phys(ret); return ret; } @@ -162,12 +169,6 @@ static inline pgd_t __pgd(unsigned long /* to align the pointer to the (next) page boundary */ #define PAGE_ALIGN(addr) (((addr)+PAGE_SIZE-1)&PAGE_MASK) - -/* See Documentation/x86_64/mm.txt for a description of the memory map. */ -#define __PHYSICAL_MASK_SHIFT 46 -#define __PHYSICAL_MASK ((1UL << __PHYSICAL_MASK_SHIFT) - 1) -#define __VIRTUAL_MASK_SHIFT 48 -#define __VIRTUAL_MASK ((1UL << __VIRTUAL_MASK_SHIFT) - 1) #define KERNEL_TEXT_SIZE (40UL*1024*1024) #define KERNEL_TEXT_START 0xffffffff80000000UL

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