Re: [PATCH, RFC 09/62] x86/mm: Preserve KeyID on pte_modify() and pgprot_modify()

[Kirill A. Shutemov]

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