Re: [PATCH] arm64: fix pud_huge() for 2-level pagetables
From: Steve Capper
Date: Thu May 15 2014 - 10:44:38 EST
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
Cheers,
--
Steve
>
> Signed-off-by: Mark Salter <msalter@xxxxxxxxxx>
> ---
> arch/arm64/mm/hugetlbpage.c | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> 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;
> --
> 1.9.0
>
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