> -----Original Message----- > From: Alexey Brodkin [mailto:abrodkin at synopsys.com] > Sent: Monday, November 28, 2016 2:43 PM > To: yuriy.kolerov at synopsys.com > Cc: linux-kernel at vger.kernel.org; Alexey.Brodkin at synopsys.com; Vineet > Gupta <vgupta at synopsys.com>; linux-snps-arc at lists.infradead.org > Subject: Re: [PATCH] ARC: mm: PAE40: Cast pfn to pte_t in pfn_pte() macro > > Hi Yuriy, > > Really nice catch! > Though a couple of nitpicks below. > > On Mon, 2016-11-28 at 07:07 +0300, Yuriy Kolerov wrote: > > Originally pfn_pte(pfn, prot) macro had this definition: > > > > ????__pte(((pfn) << PAGE_SHIFT) | pgprot_val(prot)) > > > > The value of pfn (Page Frame Number) is shifted to the left to get the > > value of pte (Page Table Entry). Usually a 4-byte value is passed to > > this macro as value of pfn. However if Linux is configured with > > support of PAE40 then value of pte has 8-byte type because it must > > contain additional 8 bits of the physical address. Thus if value of > > pfn represents a physical page frame above of 4GB boundary then > > shifting of pfn to the left by PAGE_SHIFT wipes most significant bits > > of the 40-bit physical address. > > > > As a result all physical addresses above of 4GB boundary in systems > > with PAE40 are mapped to virtual address incorrectly. An error may > > occur when the kernel tries to unmap such bad pages: > > > > ????[ECR???]: 0x00050100 => Invalid Read @ 0x41414144 by insn @ > > 0x801644c6 > > ????[EFA???]: 0x41414144 > > ????[BLINK ]: unmap_page_range+0x134/0x700 > > ????[ERET??]: unmap_page_range+0x17a/0x700 > > ????[STAT32]: 0x8008021e : IE K > > ????BTA: 0x801644c6 ?SP: 0x901a5e84 ?FP: 0x5ff35de8 > > ????LPS: 0x8026462c LPE: 0x80264630 LPC: 0x00000000 > > ????r00: 0x8fcc4fc0 r01: 0x2fe68000 r02: 0x41414140 > > ????r03: 0x2c05c000 r04: 0x2fe6a000 r05: 0x0009ffff > > ????r06: 0x901b6898 r07: 0x2fe68000 r08: 0x00000001 > > ????r09: 0x804a807c r10: 0x0000067e r11: 0xffffffff > > ????r12: 0x80164480 > > ????Stack Trace: > > ??????unmap_page_range+0x17a/0x700 > > ??????unmap_vmas+0x46/0x64 > > ??????do_munmap+0x210/0x450 > > ??????SyS_munmap+0x2c/0x50 > > ??????EV_Trap+0xfc/0x100 > > This example makes not much sense in its current form. > I'd like to see how mentioned above problem leads to this failure. I.e. pfn = > 0xXXX gave pte = 0xYYY and at truncated to 0xYYY address there's no data we > expected thus reading from?0x41414144 end up in exception etc. > > > So the value of pfn must be casted to pte_t before shifting to ensure > > that 40-bit address will not be truncated: > > > > ????__pte(((pte_t) (pfn) << PAGE_SHIFT) | pgprot_val(prot)) > > > > Signed-off-by: Yuriy Kolerov <yuriy.kolerov at synopsys.com> > > --- > > ?arch/arc/include/asm/pgtable.h | 3 ++- > > ?1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/arch/arc/include/asm/pgtable.h > > b/arch/arc/include/asm/pgtable.h index 89eeb37..77bc51c 100644 > > --- a/arch/arc/include/asm/pgtable.h > > +++ b/arch/arc/include/asm/pgtable.h > > @@ -280,7 +280,8 @@ static inline void pmd_set(pmd_t *pmdp, pte_t > > *ptep) > > > > ?#define pte_page(pte) pfn_to_page(pte_pfn(pte)) > > ?#define mk_pte(page, prot) pfn_pte(page_to_pfn(page), prot) > > -#define pfn_pte(pfn, prot) __pte(((pfn) << PAGE_SHIFT) | > pgprot_val(prot)) > > +#define pfn_pte(pfn, prot) \ > > + __pte(((pte_t) (pfn) << PAGE_SHIFT) | pgprot_val(prot)) > > I think it's better to split it in a bit different manner like: > --------------------------------->8----------------------------- > #define pfn_pte(pfn, prot) __pte(((pte_t) (pfn) << PAGE_SHIFT) | \ > ??????pgprot_val(prot)) > --------------------------------->8----------------------------- > > Also see how this macro is implemented for example on ARM: > http://lxr.free-electrons.com/source/arch/arm/include/asm/pgtable.h#L211 > -------------------->8------------------ > #define pfn_pte(pfn,prot)???????__pte(__pfn_to_phys(pfn) | > pgprot_val(prot)) > -------------------->8------------------ > > Where __pfn_to_phys() is: > http://lxr.free-electrons.com/source/include/asm- > generic/memory_model.h#L78 > -------------------->8------------------ > #define __pfn_to_phys(pfn)??????PFN_PHYS(pfn) > -------------------->8------------------ > > PFN_PHYS() is: > http://lxr.free-electrons.com/source/include/linux/pfn.h#L20 > -------------------->8------------------ > #define PFN_PHYS(x)?????((phys_addr_t)(x) << PAGE_SHIFT) > -------------------->8------------------ > > And finally phys_addr_t is: > http://lxr.free-electrons.com/source/include/linux/types.h#L161 > -------------------->8------------------ > #ifdef CONFIG_PHYS_ADDR_T_64BIT > typedef u64 phys_addr_t; > #else > typedef u32 phys_addr_t; > #endif > -------------------->8------------------ > > Not really sure though which implementation is better. > I like your approach because its simplicity instead of another couple of layers > of definitions but maybe there's a reason for this kind of complication. Funny > enough other arches take their own approaches ranging from the same you > did to this __pfn_to_phys() to casting to "long long". Yes, you are right. __pfn_to_phys() does what is needed. > -Alexey
