Messages in this thread | | | Date | Fri, 29 Aug 2008 08:30:12 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86: split e820 reserved entries record to late v4 |
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* 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'.
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.
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?
Ingo
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