On Mon, Jul 09, 2012 at 06:43:33PM +0530, Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V" <aneesh.ku...@linux.vnet.ibm.com>
>
> This patch convert different functions to take virtual page number
> instead of virtual address. Virtual page number is virtual address
> shifted right by VPN_SHIFT (12) bits. This enable us to have an
> address range of upto 76 bits.
Some comments inline below...
> +/*
> + * encode page number shift.
> + * Inorder to fit the 78 bit va in a 64 bit variable we shift the va by
^ "in order"
> + * 12 bits. This enable us to address upto 76 bit va.
^ "up to"
> + * For hpt hash from a va we can ignore the page size bits of va and for
> + * hpte encoding we ignore upto 23 bits of va. So ignoring lower 12 bits
> ensure
> + * we work in all cases including 4k page size.
> + */
> +#define VPN_SHIFT 12
This can't be more than 12 bits because we sometimes use 4k pages even
in a kernel configured for 64k pages (e.g. with the subpage_protection
system call).
> +static inline unsigned long hpte_encode_avpn(unsigned long vpn, int psize,
> + int ssize)
> +{
> + unsigned long v;
> + /*
> + * The AVA field omits the low-order 23 bits of the 78 bits VA.
> + * These bits are not needed in the PTE, because the
> + * low-order b of these bits are part of the byte offset
> + * into the virtual page and, if b < 23, the high-order
> + * 23-b of these bits are always used in selecting the
> + * PTEGs to be searched
> + */
> + BUG_ON(VPN_SHIFT > 23);
I don't think we need this. If VPN_SHIFT was computed by some complex
expression whose value is not obvious, then BUG_ON (or BUILD_BUG_ON)
would be appropriate, but since it's just a #define, a comment at the
site of the definition will suffice.
> static inline unsigned long hpt_hash(unsigned long va, unsigned int shift,
> int ssize)
> {
> + int mask;
> unsigned long hash, vsid;
>
> + BUG_ON(shift < VPN_SHIFT);
So VPN_SHIFT can be at most 12, since 12 is the smallest shift value
possible here.
> -static inline void __tlbiel(unsigned long va, int psize, int ssize)
> +static inline void __tlbiel(unsigned long vpn, int psize, int ssize)
> {
> + unsigned long va;
> unsigned int penc;
>
> + BUG_ON((77 - 65) > VPN_SHIFT);
> + va = vpn << VPN_SHIFT;
So VPN_SHIFT has to be at least 12. What is the significance of 77
and 65 here?
Paul.
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