Date: Wed, 08 Nov 2000 12:39:32 -0800 (PST) From: John Baldwin <jhb@FreeBSD.org> To: John Baldwin <jhb@FreeBSD.org> Cc: hackers@FreeBSD.org, Jeroen Ruigrok van der Werven <asmodai@FreeBSD.org> Subject: RE: PSE/PAE support Message-ID: <XFMail.001108123932.jhb@FreeBSD.org> In-Reply-To: <XFMail.001108120910.jhb@FreeBSD.org>
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On 08-Nov-00 John Baldwin wrote: > I'm sure Peter can correct this and fill in any holes as well as offer > guidance to anyone who is masochistic enough^W^Wwilling to work on this. Well, I didn't get all the facts quite right *sigh*. The page directory pointer table actually contains 4 entries which are indexed by the upper 2 bits of the virtual linear address. Also, one thing I failed to mention is that the choice between small and large pages is made via the PS bit in the page directory table entry that points to either a large page or a page table. And my table of page-sizes was a little off, it looks like this: Page Size Table: | Small Pages | Large Pages --------------------------------------- Normal | 4k | 4k PSE | 4k | 4m PAE | 4k | 2m PAE + PSE | 4k | 4m Now, if we look at how the virtual address is split up when using PAE for a large page: 31 30 29 21 20 0 ----------------------------------------------- | | | | ----------------------------------------------- ^ ^ ^ | | `----------------- offset within the page | `------------------------------------- index into the page directory `--------------------------------------------- index into the page directory pointer table This means that large pages with PAE have a 21-bit offset. That only allows for a 2mb offset, so I'm not sure how one goes about addressing the upper 2mb of a 4mb page then. *scratches head* -- John Baldwin <jhb@FreeBSD.org> -- http://www.FreeBSD.org/~jhb/ PGP Key: http://www.baldwin.cx/~john/pgpkey.asc "Power Users Use the Power to Serve!" - http://www.FreeBSD.org/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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