Re: [PATCH] arm: KVM: fix possible misalignment of PGDs and bounce page

[Marc Zyngier]

On 2014-03-28 19:37, Christoffer Dall wrote:
> 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@xxxxxxxxxx>
> > ---
> >  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@xxxxxxxxxx>
>
> If Marc agrees I can queue this for -rc1.

Looks good to me indeed.

Acked-by: Marc Zyngier <marc.zyngier@xxxxxxx>

        M.
--
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