| Message ID | fbb269c0-e915-a9f2-da3b-5ae3a2b31396@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 17/05/18 13:46, Jia He wrote: > Hi Suzuki > > On 5/17/2018 4:17 PM, Suzuki K Poulose Wrote: >> >> Hi Jia, >> >> On 17/05/18 07:11, Jia He wrote: >>> I ever met a panic under memory pressure tests(start 20 guests and run >>> memhog in the host). >> >> Please avoid using "I" in the commit description and preferably stick to >> an objective description. > > Thanks for the pointing > >> >>> >>> The root cause might be what I fixed at [1]. But from arm kvm points of >>> view, it would be better we caught the exception earlier and clearer. >>> >>> If the size is not PAGE_SIZE aligned, unmap_stage2_range might unmap the >>> wrong(more or less) page range. Hence it caused the "BUG: Bad page >>> state" >> >> I don't see why we should ever panic with a "positive" size value. Anyways, >> the unmap requests must be in units of pages. So this check might be useful. >> >> > > good question, > > After further digging, maybe we need to harden the break condition as below? > diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c > index 7f6a944..dac9b2e 100644 > --- a/virt/kvm/arm/mmu.c > +++ b/virt/kvm/arm/mmu.c > @@ -217,7 +217,7 @@ static void unmap_stage2_ptes(struct kvm *kvm, pmd_t *pmd, > > put_page(virt_to_page(pte)); > } > - } while (pte++, addr += PAGE_SIZE, addr != end); > + } while (pte++, addr += PAGE_SIZE, addr < end); I don't think this change is need as stage2_pgd_addr_end(addr, end) must return the smaller of the next entry or end. Thus we can't miss "addr" == "end". Suzuki
Hi Suzuki On 5/17/2018 11:03 PM, Suzuki K Poulose Wrote: > On 17/05/18 13:46, Jia He wrote: >> Hi Suzuki >> >> On 5/17/2018 4:17 PM, Suzuki K Poulose Wrote: >>> >>> Hi Jia, >>> >>> On 17/05/18 07:11, Jia He wrote: >>>> I ever met a panic under memory pressure tests(start 20 guests and run >>>> memhog in the host). >>> >>> Please avoid using "I" in the commit description and preferably stick to >>> an objective description. >> >> Thanks for the pointing >> >>> >>>> >>>> The root cause might be what I fixed at [1]. But from arm kvm points of >>>> view, it would be better we caught the exception earlier and clearer. >>>> >>>> If the size is not PAGE_SIZE aligned, unmap_stage2_range might unmap the >>>> wrong(more or less) page range. Hence it caused the "BUG: Bad page >>>> state" >>> >>> I don't see why we should ever panic with a "positive" size value. Anyways, >>> the unmap requests must be in units of pages. So this check might be useful. >>> >>> >> >> good question, >> >> After further digging, maybe we need to harden the break condition as below? >> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c >> index 7f6a944..dac9b2e 100644 >> --- a/virt/kvm/arm/mmu.c >> +++ b/virt/kvm/arm/mmu.c >> @@ -217,7 +217,7 @@ static void unmap_stage2_ptes(struct kvm *kvm, pmd_t *pmd, >> >> put_page(virt_to_page(pte)); >> } >> - } while (pte++, addr += PAGE_SIZE, addr != end); >> + } while (pte++, addr += PAGE_SIZE, addr < end); > > I don't think this change is need as stage2_pgd_addr_end(addr, end) must return > the smaller of the next entry or end. Thus we can't miss "addr" == "end". If it passes addr=202920000,size=fe00 to unmap_stage2_range-> ...->unmap_stage2_ptes unmap_stage2_ptes will get addr=202920000,end=20292fe00 after first while loop addr=202930000, end=20292fe00, then addr!=end Thus it will touch another pages by put_pages() in the 2nd loop.
diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c index 7f6a944..dac9b2e 100644 --- a/virt/kvm/arm/mmu.c +++ b/virt/kvm/arm/mmu.c @@ -217,7 +217,7 @@ static void unmap_stage2_ptes(struct kvm *kvm, pmd_t *pmd, put_page(virt_to_page(pte)); } - } while (pte++, addr += PAGE_SIZE, addr != end); + } while (pte++, addr += PAGE_SIZE, addr < end); basically verified in my armv8a server