Date: Tue, 02 Jan 2007 00:46:38 +0000 From: Ian Dowse <iedowse@iedowse.com> To: Matthew Dillon <dillon@apollo.backplane.com> Cc: freebsd-hackers@freebsd.org Subject: Re: Confusion in acpi_sleep_machdep(). Message-ID: <200701020046.aa80712@nowhere.iedowse.com> In-Reply-To: Your message of "Sun, 31 Dec 2006 12:43:44 PST." <200612312043.kBVKhi7t095666@apollo.backplane.com>
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In message <200612312043.kBVKhi7t095666@apollo.backplane.com>, Matthew Dillon w rites: > I'm trying to figure out how the acpi_sleep_machdep() code works and > there are a couple of lines I just don't understand: > > pm = vmspace_pmap(p->p_vmspace); > cr3 = rcr3(); >#ifdef PAE > load_cr3(vtophys(pm->pm_pdpt)); >#else > load_cr3(vtophys(pm->pm_pdir)); >#endif > > page = PHYS_TO_VM_PAGE(sc->acpi_wakephys); > pmap_enter(pm, sc->acpi_wakephys, page, > VM_PROT_READ | VM_PROT_WRITE | VM_PROT_EXECUTE, 1); > > First, why isn't it just using kernel_pmap ? What's all the load_cr3() > stuff for ? > > Second, why is it entering the physical address sc->acpi_wakephys > as the virtual address in the pmap ? Shouldn't it be using > sc->acpi_wakeaddr there? > > Anybody know ? I don't know the details, but acpi_sleep_machdep() sets up an identity mapping in the current process's vmspace (hence using virtual = physical). Lazy switching of address spaces means that cr3 may not currently refer to the same vmspace, which would break the identity mapping, so that's the reason for the load_cr3() calls. See revision 1.22 for a bit more information. Ian
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