Messages in this thread | | | Subject | Re: [PATCH 6/6] Add 32 bit VDSO support for 32 and 64 bit kernels | From | Stefani Seibold <> | Date | Thu, 20 Dec 2012 18:53:12 +0100 |
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Am Donnerstag, den 20.12.2012, 08:17 -0800 schrieb H. Peter Anvin: > The whole point is to avoid fixed addresses. We already install a list of pages as the vdso; the vvar and hpet pages can simply be part of that list. >
It would be great if you can give me a answer for my question. Again:
In a 32 bit kernel a VDSO can mapped on an fix address VDSO_HIGH_BASE (kernel parameter vdso32=2 or CONFIG_COMPAT_VDSO), which is 0xffffe000. There is no available page BEFORE nor AFTER the page, so it is not possible to have VVAR or HPET as a part of that list!!!!
> Stefani Seibold <stefani@seibold.net> wrote: > > >Am Dienstag, den 18.12.2012, 12:37 -0800 schrieb Andy Lutomirski: > >> On Tue, Dec 18, 2012 at 12:32 PM, Stefani Seibold > ><stefani@seibold.net> wrote: > >> > Am Dienstag, den 18.12.2012, 10:44 -0800 schrieb H. Peter Anvin: > >> >> On 12/18/2012 08:52 AM, Stefani Seibold wrote: > >> >> > > >> >> > Pardon, i never disregarded nor i have agreed that this is going > >to be a > >> >> > part of the VDSO. I currently have also no idea how to do this > >and i see > >> >> > no need at the moment to do this revamp. The 64 bit VDSO lives > >since > >> >> > more than 6 years with this kind of implementation. > >> >> > > >> >> > >> >> It was part of this discussion thread, about how to best manage > >the > >> >> address space. Fixed addresses are a major problem, and > >introducing new > >> >> ones are extremely undesirable. > >> >> > >> > > >> > There is no introduce of new fix address. There are still there for > >> > x86_64. If this will currently not a major problem on this > >architecture > >> > than it will not for x86_32 too. > >> > >> Not necessarily true. On x86-64 (non-compat) the fixmap address is > >in > >> kernel space (high bit set), so it can't conflict with anything in > >> user space. On true 32-bit mode, the same applies. In compat mode, > >> the fixed address is in *user* space and might conflict with existing > >> uses. > >> > >> > > >> >> Hence I wrote: > >> >> > >> >> > IMO it seems this is making it way more complicated than it is. > >Just > >> >> > make sure you have a section in the vdso where you can map in a > >data > >> >> > page with the symbols in the right offsets. Extra points for > >doing > >> >> > magic so that it is at the beginning or end, but I think that > >might > >> >> > be harder than necessary. > >> >> > >> >> Basically, make the vvar and hpet pages part of the vdso page > >list. > >> >> Optionally they can be mapped without the MAYWRITE option -- in > >fact, we > >> >> could easily split the vdso into an executable area which gets > >MAYWRITE > >> >> to be able to set breakpoints and a data area which doesn't -- but > >that > >> >> is a minor tweak IMO. > >> >> > >> > > >> > I see the benefits, but it will not work under all circumstance. > >The > >> > VDSO compat mode for x86_32 requires a fix address and there is no > >room > >> > behind this. So since this must preserved, i see no real gain for > >this. > >> > >> Not true. It can be mapped with the vdso at a variable address using > >> GOTOFF addressing. See my earlier email with > >> __attribute__((visibility("hidden")). > >> > >> --Andy > > > >I am not sure that we talking about the same. > > > >In a 32 bit kernel a VDSO can mapped on an fix address VDSO_HIGH_BASE > >(kernel parameter vdso32=2 or CONFIG_COMPAT_VDSO), which is 0xffffe000. > >There is no available page before nor after this page, so there is no > >space for a multi page VDSO. > > > >The only way i see is to do this is a test in the vdso_...() functions > >for running on this address and than access the old fixmap addresses > >for > >VVAR and HPET. This can be done for example by a tweaking macro. > > > >If this is okay, i can do it. Otherwise i have no idea how to. > > > >- Stefani >
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