Messages in this thread | | | Date | Thu, 28 Aug 2008 23:47:14 -0700 | From | "Yinghai Lu" <> | Subject | Re: [PATCH] x86: split e820 reserved entries record to late v4 |
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On Thu, Aug 28, 2008 at 11:30 PM, Ingo Molnar <mingo@elte.hu> wrote: > > * Yinghai Lu <yhlu.kernel@gmail.com> wrote: > >> Linus said we should register some entries in e820 later, >> so could let BAR res register at first, or even pnp? >> >> this one replace >> | commit a2bd7274b47124d2fc4dfdb8c0591f545ba749dd >> | Author: Yinghai Lu <yhlu.kernel@gmail.com> >> | Date: Mon Aug 25 00:56:08 2008 -0700 >> | >> | x86: fix HPET regression in 2.6.26 versus 2.6.25, check hpet against BAR, v3 >> >> v2: insert e820 reserve resources before pnp_system_init >> v3: fix merging problem in tip/x86/core >> please drop the one in tip/x86/core use this one instead >> v4: address Linus's review about comments and condition in _late() >> >> Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com> > > applied to tip/x86/core, thanks. > > Let me outline the issue that i raised before: > >> + if (!res->parent && res->end) >> + insert_resource(&iomem_resource, res); > > what if this insertion fails due to partial overlap? Right now we drop > it silently - which might be fine for most systems, but have a look on > the specific system that had the hpet regression, there we have these > reserved e820 entries: > > BIOS-e820: 0000000077ff0000 - 0000000078000000 (reserved) > BIOS-e820: 00000000e0000000 - 00000000f0000000 (reserved) > BIOS-e820: 00000000fec00000 - 0000000100000000 (reserved) > > which overlaps with the chipset PCI BAR (hpet) resource: > > pci 0000:00:14.0: BAR has HPET at fed00000-fed003ff > > so due to this 1K conflict we take the full e820-reserved entry out and > give the range 0xfec00000-0x100000000 as 'free'.
you will get fec00000 - ffffffff reserved fed0000 - fed003ff hpet fed0000 - fed003ff 0000:00:14.0
> > And that failure to register can cause problems. In this case that > 'reserved' e820 entry definitely has real meaning, both the local APIC > and the IO-APIC is in that range: > > ACPI: Local APIC address 0xfee00000 > IOAPIC[0]: apic_id 2, version 0, address 0xfec00000, GSI 0-23 > > Which might still be OK for all memory resources we happen to enumerate > - but we dont necessarily enumerate all of them when we have e.g. an UP > kernel, and we will definitely not enumerate any 'hidden' state a system > might have there. (SMM, etc.) If we then allocate a dynamic PCI resource > into that range later on (thinking it's "free" but in reality it's > claimed) we get a crash or worse. > > So my worry, which i outlined before and which Peter agreed with, was > that we should not mark areas 'free' that the BIOS thinks are > 'reserved'. According to the map above, the BIOS declared non-RAM 'free' > range in the first 4GB is 0x78000000..0xe0000000 - 1664 MB, plenty of > space.
for the pci gap use? e820_setup_gap will check e820_map directly to use that range as pci gap for unassigned resources.
> > The solution would be to insert such conflicting (even if partially > overlapping) > > Also, a small code structure comment: > >> + if (e820.map[i].type != E820_RESERVED || res->start < (1ULL<<20)) >> + insert_resource(&iomem_resource, res); > > this still needs a comment that we deal with resources that start below > 1MB in a special way and insert them early. > > Perhaps split it out into a e820_entry_trusted() function and use that > as a condition in both the early and the late logic. [plus the check for > ->end in the late logic - that should be outside of the 'trust' > definition] > > So whenever we tweak the definition of 'trust', we only have to do it in > a single place. Agreed?
yes
YH
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