From a987370f8e7a1677ae385042644326d9cd145a20 Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Tue, 10 Mar 2015 19:06:59 +0000 Subject: arm64: KVM: Fix stage-2 PGD allocation to have per-page refcounting We're using __get_free_pages with to allocate the guest's stage-2 PGD. The standard behaviour of this function is to return a set of pages where only the head page has a valid refcount. This behaviour gets us into trouble when we're trying to increment the refcount on a non-head page: page:ffff7c00cfb693c0 count:0 mapcount:0 mapping: (null) index:0x0 flags: 0x4000000000000000() page dumped because: VM_BUG_ON_PAGE((*({ __attribute__((unused)) typeof((&page->_count)->counter) __var = ( typeof((&page->_count)->counter)) 0; (volatile typeof((&page->_count)->counter) *)&((&page->_count)->counter); })) <= 0) BUG: failure at include/linux/mm.h:548/get_page()! Kernel panic - not syncing: BUG! CPU: 1 PID: 1695 Comm: kvm-vcpu-0 Not tainted 4.0.0-rc1+ #3825 Hardware name: APM X-Gene Mustang board (DT) Call trace: [] dump_backtrace+0x0/0x13c [] show_stack+0x10/0x1c [] dump_stack+0x74/0x94 [] panic+0x100/0x240 [] stage2_get_pmd+0x17c/0x2bc [] kvm_handle_guest_abort+0x4b4/0x6b0 [] handle_exit+0x58/0x180 [] kvm_arch_vcpu_ioctl_run+0x114/0x45c [] kvm_vcpu_ioctl+0x2e0/0x754 [] do_vfs_ioctl+0x424/0x5c8 [] SyS_ioctl+0x40/0x78 CPU0: stopping A possible approach for this is to split the compound page using split_page() at allocation time, and change the teardown path to free one page at a time. It turns out that alloc_pages_exact() and free_pages_exact() does exactly that. While we're at it, the PGD allocation code is reworked to reduce duplication. This has been tested on an X-Gene platform with a 4kB/48bit-VA host kernel, and kvmtool hacked to place memory in the second page of the hardware PGD (PUD for the host kernel). Also regression-tested on a Cubietruck (Cortex-A7). [ Reworked to use alloc_pages_exact() and free_pages_exact() and to return pointers directly instead of by reference as arguments - Christoffer ] Reported-by: Mark Rutland Signed-off-by: Marc Zyngier Signed-off-by: Christoffer Dall --- arch/arm/include/asm/kvm_mmu.h | 10 ++++------ 1 file changed, 4 insertions(+), 6 deletions(-) (limited to 'arch/arm/include') diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h index bf0fe99e8ca9..c57c41dc7e87 100644 --- a/arch/arm/include/asm/kvm_mmu.h +++ b/arch/arm/include/asm/kvm_mmu.h @@ -162,16 +162,14 @@ static inline bool kvm_page_empty(void *ptr) #define KVM_PREALLOC_LEVEL 0 -static inline int kvm_prealloc_hwpgd(struct kvm *kvm, pgd_t *pgd) +static inline void *kvm_get_hwpgd(struct kvm *kvm) { - return 0; + return kvm->arch.pgd; } -static inline void kvm_free_hwpgd(struct kvm *kvm) { } - -static inline void *kvm_get_hwpgd(struct kvm *kvm) +static inline unsigned int kvm_get_hwpgd_size(void) { - return kvm->arch.pgd; + return PTRS_PER_S2_PGD * sizeof(pgd_t); } struct kvm; -- cgit v1.2.3