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SubjectRe: [PATCH, RFC 09/62] x86/mm: Preserve KeyID on pte_modify() and pgprot_modify()
On Fri, Jun 14, 2019 at 11:15:14AM +0200, Peter Zijlstra wrote:
> On Wed, May 08, 2019 at 05:43:29PM +0300, Kirill A. Shutemov wrote:
> > + * Cast PAGE_MASK to a signed type so that it is sign-extended if
> > + * virtual addresses are 32-bits but physical addresses are larger
> > + * (ie, 32-bit PAE).
>
> On 32bit, 'long' is still 32bit, did you want to cast to 'long long'
> instead? Ideally we'd use pteval_t here, but I see that is unsigned.

It will be cased implecitly to unsigned long long by '& ((1ULL <<
__PHYSICAL_MASK_SHIFT) - 1)' and due to sign-extension it will get it
right for PAE.

Just to be on safe side, I've re-checked that nothing changed for PAE by
the patch using the test below. PTE_PFN_MASK and PTE_PFN_MASK_MAX are
identical when compiled with -m32.

> > */
> > -#define _PAGE_CHG_MASK (PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT | \
> > +#define PTE_PFN_MASK_MAX \
> > + (((signed long)PAGE_MASK) & ((1ULL << __PHYSICAL_MASK_SHIFT) - 1))
> > +#define _PAGE_CHG_MASK (PTE_PFN_MASK_MAX | _PAGE_PCD | _PAGE_PWT | \
> > _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY | \
> > _PAGE_SOFT_DIRTY | _PAGE_DEVMAP)
> > #define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE)
>

#include <stdio.h>

typedef unsigned long long u64;
typedef u64 pteval_t;
typedef u64 phys_addr_t;

#define PAGE_SHIFT 12
#define PAGE_SIZE (1UL << PAGE_SHIFT)
#define PAGE_MASK (~(PAGE_SIZE-1))
#define __PHYSICAL_MASK_SHIFT 52
#define __PHYSICAL_MASK ((phys_addr_t)((1ULL << __PHYSICAL_MASK_SHIFT) - 1))
#define PHYSICAL_PAGE_MASK (((signed long)PAGE_MASK) & __PHYSICAL_MASK)
#define PTE_PFN_MASK ((pteval_t)PHYSICAL_PAGE_MASK)
#define PTE_PFN_MASK_MAX (((signed long)PAGE_MASK) & ((1ULL << __PHYSICAL_MASK_SHIFT) - 1))

int main(void)
{
printf("PTE_PFN_MASK: %#llx\n", PTE_PFN_MASK);
printf("PTE_PFN_MASK_MAX: %#llx\n", PTE_PFN_MASK_MAX);

return 0;
}
--
Kirill A. Shutemov

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