Date: Mon, 21 Apr 2003 11:33:22 -0700 From: Marcel Moolenaar <marcel@xcllnt.net> To: Jake Burkholder <jake@locore.ca> Cc: freebsd-hackers@freebsd.org Subject: Re: Is pmap_kextract() allowed to fault? Message-ID: <20030421183322.GA557@dhcp01.pn.xcllnt.net> In-Reply-To: <20030421132449.GA50754@locore.ca> References: <20030421055332.GA4680@dhcp01.pn.xcllnt.net> <20030421132449.GA50754@locore.ca>
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On Mon, Apr 21, 2003 at 09:24:49AM -0400, Jake Burkholder wrote: > Apparently, On Sun, Apr 20, 2003 at 10:53:32PM -0700, > Marcel Moolenaar said words to the effect of; > > > Gang, > > > > On ia64 pmap_kextract() uses the tpa instruction which given a > > virtual address returns the physical address based on the > > translation registers and cache (ie TLB). This can fault when > > there's currently no mapping for the virtual address. > > > > Since all other architectures have a non-faulting implementation > > (AFAICT), I'm a bit worried that we might get into trouble on > > ia64. I couldn't find anything about pmap_kextract(), so maybe > > anybody can enlighten me: > > > > 1. Is pmap_kextract() allowed to fault? > > It depends what kind of fault. Will tpa fail if it causes a tlb fault > and the page is not in the vhpt (or whatever the fault handler searches), > or will it end up calling vm_fault and actually trying to fault in the > page? It will end up calling vm_fault() if so required. > > 2. Is pmap_kextract() used often enough that using the cpu's TLB > > is a possible performance speedup even if there are costly faults > > that can sometimes happen? > > I doubt it. Ok, thanks. I think I'll use a non-trapping implementation then. There's just too much circumstantiality... -- Marcel Moolenaar USPA: A-39004 marcel@xcllnt.net
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