Re: [PATCH V3 08/30] x86/sgx: Move PTE zap code to new sgx_zap_enclave_ptes()

Jarkko Sakkinen
2022-04-05T06:58:36Z

On Mon, Apr 04, 2022 at 09:49:16AM -0700, Reinette Chatre wrote:
> The SGX reclaimer removes page table entries pointing to pages that are
> moved to swap.
>
> SGX2 enables changes to pages belonging to an initialized enclave, thus
> enclave pages may have their permission or type changed while the page
> is being accessed by an enclave. Supporting SGX2 requires page table
> entries to be removed so that any cached mappings to changed pages
> are removed. For example, with the ability to change enclave page types
> a regular enclave page may be changed to a Thread Control Structure
> (TCS) page that may not be accessed by an enclave.
>
> Factor out the code removing page table entries to a separate function
> sgx_zap_enclave_ptes(), fixing accuracy of comments in the process,
> and make it available to the upcoming SGX2 code.
>
> Place sgx_zap_enclave_ptes() with the rest of the enclave code in
> encl.c interacting with the page table since this code is no longer
> unique to the reclaimer.
>
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
> ---
> No changes since V2
>
> Changes since V1:
> - Elaborate why SGX2 needs this ability (Jarkko).
> - More specific subject.
> - Fix kernel-doc to have brackets in function name.
>
> arch/x86/kernel/cpu/sgx/encl.c | 45 +++++++++++++++++++++++++++++++++-
> arch/x86/kernel/cpu/sgx/encl.h | 2 +-
> arch/x86/kernel/cpu/sgx/main.c | 31 ++---------------------
> 3 files changed, 47 insertions(+), 31 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> index 8de9bebc4d81..c77a62432862 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -605,7 +605,7 @@ int sgx_encl_mm_add(struct sgx_encl *encl, struct mm_struct *mm)
>
> spin_lock(&encl->mm_lock);
> list_add_rcu(&encl_mm->list, &encl->mm_list);
> - /* Pairs with smp_rmb() in sgx_reclaimer_block(). */
> + /* Pairs with smp_rmb() in sgx_zap_enclave_ptes(). */
> smp_wmb();
> encl->mm_list_version++;
> spin_unlock(&encl->mm_lock);
> @@ -792,6 +792,49 @@ int sgx_encl_test_and_clear_young(struct mm_struct *mm,
> return ret;
> }
>
> +/**
> + * sgx_zap_enclave_ptes() - remove PTEs mapping the address from enclave
> + * @encl: the enclave
> + * @addr: page aligned pointer to single page for which PTEs will be removed
> + *
> + * Multiple VMAs may have an enclave page mapped. Remove the PTE mapping
> + * @addr from each VMA. Ensure that page fault handler is ready to handle
> + * new mappings of @addr before calling this function.
> + */
> +void sgx_zap_enclave_ptes(struct sgx_encl *encl, unsigned long addr)
> +{
> + unsigned long mm_list_version;
> + struct sgx_encl_mm *encl_mm;
> + struct vm_area_struct *vma;
> + int idx, ret;
> +
> + do {
> + mm_list_version = encl->mm_list_version;
> +
> + /* Pairs with smp_wmb() in sgx_encl_mm_add(). */
> + smp_rmb();
> +
> + idx = srcu_read_lock(&encl->srcu);
> +
> + list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) {
> + if (!mmget_not_zero(encl_mm->mm))
> + continue;
> +
> + mmap_read_lock(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);
> +
> + mmap_read_unlock(encl_mm->mm);
> +
> + mmput_async(encl_mm->mm);
> + }
> +
> + srcu_read_unlock(&encl->srcu, idx);
> + } while (unlikely(encl->mm_list_version != mm_list_version));
> +}
> +
> /**
> * sgx_alloc_va_page() - Allocate a Version Array (VA) page
> *
> diff --git a/arch/x86/kernel/cpu/sgx/encl.h b/arch/x86/kernel/cpu/sgx/encl.h
> index e59c2cbf71e2..1b15d22f6757 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.h
> +++ b/arch/x86/kernel/cpu/sgx/encl.h
> @@ -111,7 +111,7 @@ int sgx_encl_get_backing(struct sgx_encl *encl, unsigned long page_index,
> void sgx_encl_put_backing(struct sgx_backing *backing, bool do_write);
> int sgx_encl_test_and_clear_young(struct mm_struct *mm,
> struct sgx_encl_page *page);
> -
> +void sgx_zap_enclave_ptes(struct sgx_encl *encl, unsigned long addr);
> struct sgx_epc_page *sgx_alloc_va_page(void);
> unsigned int sgx_alloc_va_slot(struct sgx_va_page *va_page);
> void sgx_free_va_slot(struct sgx_va_page *va_page, unsigned int offset);
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index fa33922879bf..ce9e87d5f8ec 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -137,36 +137,9 @@ static void sgx_reclaimer_block(struct sgx_epc_page *epc_page)
> struct sgx_encl_page *page = epc_page->owner;
> unsigned long addr = page->desc & PAGE_MASK;
> 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;
> -
> - do {
> - mm_list_version = encl->mm_list_version;
> -
> - /* Pairs with smp_rmb() in sgx_encl_mm_add(). */
> - smp_rmb();
> -
> - idx = srcu_read_lock(&encl->srcu);
> -
> - list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) {
> - if (!mmget_not_zero(encl_mm->mm))
> - continue;
> -
> - mmap_read_lock(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);
> -
> - mmap_read_unlock(encl_mm->mm);
> -
> - mmput_async(encl_mm->mm);
> - }
> + int ret;
>
> - srcu_read_unlock(&encl->srcu, idx);
> - } while (unlikely(encl->mm_list_version != mm_list_version));
> + sgx_zap_enclave_ptes(encl, addr);
>
> mutex_lock(&encl->lock);
>
> --
> 2.25.1
>

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

BR, Jarkko