On Thu, Jun 10, 2021 at 07:11:53AM -0700, Dave Hansen wrote: > On 6/10/21 2:01 AM, Jarkko Sakkinen wrote: > > On Thu, Jun 10, 2021 at 10:21:17AM +0300, Jarkko Sakkinen wrote: > >> For uninitialized data, there's a need to add the same page multiple times, > >> e.g. a zero page, instead of traversing the source memory forward. With the > >> current API, this requires to call SGX_IOC_ENCLAVE_ADD_PAGES multiple > >> times, once per page, which is not very efficient. > >> > >> Add a new SGX_PAGE_REPEAT flag to resolve the issue. When this flag is set > >> to the 'flags' field of struct sgx_enclave_pages, the ioctl will apply the > >> page at 'src' multiple times, instead of moving forward in the address > >> space. > >> > >> Signed-off-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx> > > After sending this, I started to think that maybe it would actually better > > to just add SGX_PAGE_ZERO flag, i.e. add zero pages and ignore src. That's > > the main use case right now, and saves the user space from extra trouble of > > having to do such page by hand. > > > > That neither does prevent adding SGX_PAGE_REPEAT later on. I just see no > > point of that generic functionality right now. It only makes simple use > > case more complex. > > Is the main argument behind this new ABI that it increases efficiency? > > Let's say I want to add 1MB of 0'd pages to an enclave. Won't this do it? > > zeros = mmap(NULL, size, PROT_READ, MAP_ANONYMOUS|MAP_PRIVATE, > -1, 0); > ioctl(SGX_IOC_ENCLAVE_ADD_PAGES, zeros, size); Later, with LSM's, it's better to mmap /dev/null. > Sure, you'll pay the cost of faulting in the zero page size/PAGE_SIZE > times. But, that's pretty minuscule. This zeros buffer can also be > reused without faulting again. It can be as big or small as you want. > Heck, it could even be 2MB in size and use the transparent huge page. > > I agree that there's definitely some optimization work to do. But, I'm > a bit hesitant to turn to new ABI to do it. I realized that it's good to create heap memory like in your example because then any possible SGX_IOC_ENCLAVE_ADD_PAGES invocation map to LSM rules, i.e. every call has a well-defined source. /Jarkko
