| Message ID | 1400163562-7481-1-git-send-email-msalter@redhat.com |
|---|---|
| State | Accepted |
| Commit | 4797ec2dc83a43be35bad56037d1b53db9e2b5d5 |
| Headers | show |
On 15 May 2014 17:27, Mark Salter <msalter@redhat.com> wrote: > On Thu, 2014-05-15 at 15:44 +0100, Steve Capper wrote: >> On Thu, May 15, 2014 at 10:19:22AM -0400, Mark Salter wrote: >> > The following happens when trying to run a kvm guest on a kernel >> > configured for 64k pages. This doesn't happen with 4k pages: >> > >> > BUG: failure at include/linux/mm.h:297/put_page_testzero()! >> > Kernel panic - not syncing: BUG! >> > CPU: 2 PID: 4228 Comm: qemu-system-aar Tainted: GF 3.13.0-0.rc7.31.sa2.k32v1.aarch64.debug #1 >> > Call trace: >> > [<fffffe0000096034>] dump_backtrace+0x0/0x16c >> > [<fffffe00000961b4>] show_stack+0x14/0x1c >> > [<fffffe000066e648>] dump_stack+0x84/0xb0 >> > [<fffffe0000668678>] panic+0xf4/0x220 >> > [<fffffe000018ec78>] free_reserved_area+0x0/0x110 >> > [<fffffe000018edd8>] free_pages+0x50/0x88 >> > [<fffffe00000a759c>] kvm_free_stage2_pgd+0x30/0x40 >> > [<fffffe00000a5354>] kvm_arch_destroy_vm+0x18/0x44 >> > [<fffffe00000a1854>] kvm_put_kvm+0xf0/0x184 >> > [<fffffe00000a1938>] kvm_vm_release+0x10/0x1c >> > [<fffffe00001edc1c>] __fput+0xb0/0x288 >> > [<fffffe00001ede4c>] ____fput+0xc/0x14 >> > [<fffffe00000d5a2c>] task_work_run+0xa8/0x11c >> > [<fffffe0000095c14>] do_notify_resume+0x54/0x58 >> > >> > In arch/arm/kvm/mmu.c:unmap_range(), we end up doing an extra put_page() >> > on the stage2 pgd which leads to the BUG in put_page_testzero(). This >> > happens because a pud_huge() test in unmap_range() returns true when it >> > should always be false with 2-level pages tables used by 64k pages. >> > This patch removes support for huge puds if 2-level pagetables are >> > being used. >> >> Hi Mark, >> I'm still catching up with myself, sorry (was off sick for a couple >> of days)... >> >> I thought unmap_range was going to be changed? >> Does the following help things? >> https://lists.cs.columbia.edu/pipermail/kvmarm/2014-May/009388.html > > No, I get the same BUG. Regardless, pud_huge() should always return > false for 2-level pagetables, right? Okay, thanks for giving that a go. Yeah I agree for 64K granule it doesn't make sense to have a huge_pud. The patch looks sound now, but checking for a folded pmd may run into problems if/when we get to 3-levels and 64K pages in future. Perhaps checking for PAGE_SHIFT==12 (or something similar) would be a bit more robust? Cheers,
diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c index 5e9aec3..9bed38f 100644 --- a/arch/arm64/mm/hugetlbpage.c +++ b/arch/arm64/mm/hugetlbpage.c @@ -51,7 +51,11 @@ int pmd_huge(pmd_t pmd) int pud_huge(pud_t pud) { +#ifndef __PAGETABLE_PMD_FOLDED return !(pud_val(pud) & PUD_TABLE_BIT); +#else + return 0; +#endif } int pmd_huge_support(void) @@ -64,8 +68,10 @@ static __init int setup_hugepagesz(char *opt) unsigned long ps = memparse(opt, &opt); if (ps == PMD_SIZE) { hugetlb_add_hstate(PMD_SHIFT - PAGE_SHIFT); +#ifndef __PAGETABLE_PMD_FOLDED } else if (ps == PUD_SIZE) { hugetlb_add_hstate(PUD_SHIFT - PAGE_SHIFT); +#endif } else { pr_err("hugepagesz: Unsupported page size %lu M\n", ps >> 20); return 0;
The following happens when trying to run a kvm guest on a kernel configured for 64k pages. This doesn't happen with 4k pages: BUG: failure at include/linux/mm.h:297/put_page_testzero()! Kernel panic - not syncing: BUG! CPU: 2 PID: 4228 Comm: qemu-system-aar Tainted: GF 3.13.0-0.rc7.31.sa2.k32v1.aarch64.debug #1 Call trace: [<fffffe0000096034>] dump_backtrace+0x0/0x16c [<fffffe00000961b4>] show_stack+0x14/0x1c [<fffffe000066e648>] dump_stack+0x84/0xb0 [<fffffe0000668678>] panic+0xf4/0x220 [<fffffe000018ec78>] free_reserved_area+0x0/0x110 [<fffffe000018edd8>] free_pages+0x50/0x88 [<fffffe00000a759c>] kvm_free_stage2_pgd+0x30/0x40 [<fffffe00000a5354>] kvm_arch_destroy_vm+0x18/0x44 [<fffffe00000a1854>] kvm_put_kvm+0xf0/0x184 [<fffffe00000a1938>] kvm_vm_release+0x10/0x1c [<fffffe00001edc1c>] __fput+0xb0/0x288 [<fffffe00001ede4c>] ____fput+0xc/0x14 [<fffffe00000d5a2c>] task_work_run+0xa8/0x11c [<fffffe0000095c14>] do_notify_resume+0x54/0x58 In arch/arm/kvm/mmu.c:unmap_range(), we end up doing an extra put_page() on the stage2 pgd which leads to the BUG in put_page_testzero(). This happens because a pud_huge() test in unmap_range() returns true when it should always be false with 2-level pages tables used by 64k pages. This patch removes support for huge puds if 2-level pagetables are being used. Signed-off-by: Mark Salter <msalter@redhat.com> --- arch/arm64/mm/hugetlbpage.c | 6 ++++++ 1 file changed, 6 insertions(+)