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SubjectRe: [PATCH] arm: KVM: fix possible misalignment of PGDs and bounce page
On Fri, Mar 28, 2014 at 10:25:19AM -0400, Mark Salter wrote:
> The kvm/mmu code shared by arm and arm64 uses kalloc() to allocate
> a bounce page (if hypervisor init code crosses page boundary) and
> hypervisor PGDs. The problem is that kalloc() does not guarantee
> the proper alignment. In the case of the bounce page, the page sized
> buffer allocated may also cross a page boundary negating the purpose
> and leading to a hang during kvm initialization. Likewise the PGDs
> allocated may not meet the minimum alignment requirements of the
> underlying MMU. This patch uses __get_free_page() to guarantee the
> worst case alignment needs of the bounce page and PGDs on both arm
> and arm64.
>
> Signed-off-by: Mark Salter <msalter@redhat.com>
> ---
> arch/arm/kvm/mmu.c | 15 +++++++++------
> 1 file changed, 9 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 7789857..575d790 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -42,6 +42,8 @@ static unsigned long hyp_idmap_start;
> static unsigned long hyp_idmap_end;
> static phys_addr_t hyp_idmap_vector;
>
> +#define pgd_order get_order(PTRS_PER_PGD * sizeof(pgd_t))
> +
> #define kvm_pmd_huge(_x) (pmd_huge(_x) || pmd_trans_huge(_x))
>
> static void kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa)
> @@ -199,14 +201,14 @@ void free_boot_hyp_pgd(void)
> if (boot_hyp_pgd) {
> unmap_range(NULL, boot_hyp_pgd, hyp_idmap_start, PAGE_SIZE);
> unmap_range(NULL, boot_hyp_pgd, TRAMPOLINE_VA, PAGE_SIZE);
> - kfree(boot_hyp_pgd);
> + free_pages((unsigned long)boot_hyp_pgd, pgd_order);
> boot_hyp_pgd = NULL;
> }
>
> if (hyp_pgd)
> unmap_range(NULL, hyp_pgd, TRAMPOLINE_VA, PAGE_SIZE);
>
> - kfree(init_bounce_page);
> + free_page((unsigned long)init_bounce_page);
> init_bounce_page = NULL;
>
> mutex_unlock(&kvm_hyp_pgd_mutex);
> @@ -236,7 +238,7 @@ void free_hyp_pgds(void)
> for (addr = VMALLOC_START; is_vmalloc_addr((void*)addr); addr += PGDIR_SIZE)
> unmap_range(NULL, hyp_pgd, KERN_TO_HYP(addr), PGDIR_SIZE);
>
> - kfree(hyp_pgd);
> + free_pages((unsigned long)hyp_pgd, pgd_order);
> hyp_pgd = NULL;
> }
>
> @@ -930,7 +932,7 @@ int kvm_mmu_init(void)
> size_t len = __hyp_idmap_text_end - __hyp_idmap_text_start;
> phys_addr_t phys_base;
>
> - init_bounce_page = kmalloc(PAGE_SIZE, GFP_KERNEL);
> + init_bounce_page = (void *)__get_free_page(GFP_KERNEL);
> if (!init_bounce_page) {
> kvm_err("Couldn't allocate HYP init bounce page\n");
> err = -ENOMEM;
> @@ -956,8 +958,9 @@ int kvm_mmu_init(void)
> (unsigned long)phys_base);
> }
>
> - hyp_pgd = kzalloc(PTRS_PER_PGD * sizeof(pgd_t), GFP_KERNEL);
> - boot_hyp_pgd = kzalloc(PTRS_PER_PGD * sizeof(pgd_t), GFP_KERNEL);
> + hyp_pgd = (pgd_t *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, pgd_order);
> + boot_hyp_pgd = (pgd_t *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, pgd_order);
> +
> if (!hyp_pgd || !boot_hyp_pgd) {
> kvm_err("Hyp mode PGD not allocated\n");
> err = -ENOMEM;
> --
> 1.8.5.3
>
This looks right to me. Funnily enough I seem to remember a discussion
from when we originally merged this code where someone (maybe me) argued
that kmalloc() would align to the size of the allocation, but I don't
see anything backing this up at this point.

So:

Acked-by: Christoffer Dall <christoffer.dall@linaro.org>

If Marc agrees I can queue this for -rc1.


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