On Mon, Apr 06, 2020 at 11:56:26PM +0300, Jarkko Sakkinen wrote:
> From: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
spin_lock(&encl->mm_lock);
> +
> list_add_rcu(&encl_mm->list, &encl->mm_list);
> - spin_unlock(&encl->mm_lock);
>
> - synchronize_srcu(&encl->srcu);
> + /* Even if the CPU does not reorder writes, a compiler might. */
The preferred (by maintainers) style of comment for smp_wmb()/smp_rmb()
comments is to explicitly call out the associated reader/writer. If you
want to go with a minimal comment, my vote is for something like:
/*
* Add to list before updating version. Pairs the with smp_rmb() in
* sgx_reclaimer_block().
*/
And if you want to go really spartan, I'd take:
/* Pairs with smp_rmb() in sgx_reclaimer_block(). */
over a generic comment about the compiler reordering instructions.
> + smp_wmb();
> + encl->mm_list_version++;
> +
> + spin_unlock(&encl->mm_lock);
>
> return 0;
> }
> diff --git a/arch/x86/kernel/cpu/sgx/encl.h b/arch/x86/kernel/cpu/sgx/encl.h
> index 44b353aa8866..f0f72e591244 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.h
> +++ b/arch/x86/kernel/cpu/sgx/encl.h
> @@ -74,6 +74,7 @@ struct sgx_encl {
> struct mutex lock;
> struct list_head mm_list;
> spinlock_t mm_lock;
> + unsigned long mm_list_version;
> struct file *backing;
> struct kref refcount;
> struct srcu_struct srcu;
> diff --git a/arch/x86/kernel/cpu/sgx/reclaim.c b/arch/x86/kernel/cpu/sgx/reclaim.c
> index 39f0ddefbb79..5e089f0db201 100644
> --- a/arch/x86/kernel/cpu/sgx/reclaim.c
> +++ b/arch/x86/kernel/cpu/sgx/reclaim.c
> @@ -184,28 +184,39 @@ static void sgx_reclaimer_block(struct sgx_epc_page *epc_page)
> struct sgx_encl_page *page = epc_page->owner;
> unsigned long addr = SGX_ENCL_PAGE_ADDR(page);
> struct sgx_encl *encl = page->encl;
> + unsigned long mm_list_version;
> struct sgx_encl_mm *encl_mm;
> struct vm_area_struct *vma;
> int idx, ret;
>
> - idx = srcu_read_lock(&encl->srcu);
> + do {
> + mm_list_version = encl->mm_list_version;
>
> - list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) {
> - if (!mmget_not_zero(encl_mm->mm))
> - continue;
> + /*
> + * Fence the read. This guarantees that we don't mutate the old
> + * list with a new version.
> + */
As above, would prefer something like:
/*
* Read the version before walking the list. Pairs with the
* smp_wmb() in sgx_encl_mm_add().
*/
or just
/* Pairs with the smp_wmb() in sgx_encl_mm_add(). */
> + smp_rmb();
>
> - down_read(&encl_mm->mm->mmap_sem);
> + idx = srcu_read_lock(&encl->srcu);
>
> - ret = sgx_encl_find(encl_mm->mm, addr, &vma);
> - if (!ret && encl == vma->vm_private_data)
> - zap_vma_ptes(vma, addr, PAGE_SIZE);
> + list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) {
> + if (!mmget_not_zero(encl_mm->mm))
> + continue;
>
> - up_read(&encl_mm->mm->mmap_sem);
> + down_read(&encl_mm->mm->mmap_sem);
>
> - mmput_async(encl_mm->mm);
> - }
> + ret = sgx_encl_find(encl_mm->mm, addr, &vma);
> + if (!ret && encl == vma->vm_private_data)
> + zap_vma_ptes(vma, addr, PAGE_SIZE);
>
> - srcu_read_unlock(&encl->srcu, idx);
> + up_read(&encl_mm->mm->mmap_sem);
> +
> + mmput_async(encl_mm->mm);
> + }
> +
> + srcu_read_unlock(&encl->srcu, idx);
> + } while (unlikely(encl->mm_list_version != mm_list_version));
>
> mutex_lock(&encl->lock);
>
> @@ -250,6 +261,11 @@ static const cpumask_t *sgx_encl_ewb_cpumask(struct sgx_encl *encl)
> struct sgx_encl_mm *encl_mm;
> int idx;
>
> + /*
> + * Can race with sgx_encl_mm_add(), but ETRACK has already been
> + * executed, which means that the CPUs running in the new mm will enter
> + * into the enclave with a fresh epoch.
> + */
> cpumask_clear(cpumask);
>
> idx = srcu_read_lock(&encl->srcu);
> --
> 2.25.1
>
