Date: Mon, 31 Mar 2003 02:49:30 -0600 (CST) From: Mike Silbersack <silby@silby.com> To: Jake Burkholder <jake@locore.ca> Cc: cvs-all@FreeBSD.org Subject: Re: HEADS UP Re: cvs commit: src/sys/conf options.i386 src/sys/i386/i386 bios.c locore.s machdep.c mpboot.s pmap.c vm86bios.s vm_machdep.c src/sys/i386/include _types.h bus_at386.h param.h pmap. Message-ID: <20030330235551.L8771@odysseus.silby.com> In-Reply-To: <20030331052928.GC32298@locore.ca> References: <200303300524.h2U5Ora7061852@repoman.freebsd.org> <20030330201113.GA32298@locore.ca><20030330232030.GB32298@locore.ca> <20030331052928.GC32298@locore.ca>
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On Mon, 31 Mar 2003, Jake Burkholder wrote: > PAE makes the page table entries bigger so they can hold 64 bit physical > addresses, but it does not give you more of them, pointers are still 32bit. > On x86 the kernel is mapped into each process' address space, which is why > it takes a chunk of it, and this is how copyin and copyout work, you can > just access the current process' address space directly. All copyin and > copyout do on x86 is handle page faults due to unmapped user memory, which > should not normally happen in kernel mode. If they were separate this would > be much more complicated, and entering the kernel would require switching > address space, instead of just increasing the priviledge level. > > Jake Doh, that makes perfect sense, I didn't think it through before asking. Changing it around to have seperate address spaces sounds like more work than PAE, now that I think more about it. I'll just wait for true 64 bit machines before asking for a large KVA. :) Thanks for the explanation, Mike "Silby" Silbersack
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