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    SubjectRe: [RFC PATCH 3/9] x86/sgx: Allow userspace to add multiple pages in single ioctl()
    On Mon, Jun 3, 2019 at 1:39 PM Sean Christopherson
    <sean.j.christopherson@intel.com> wrote:
    >
    > On Mon, Jun 03, 2019 at 01:08:04PM -0700, Sean Christopherson wrote:
    > > On Sun, Jun 02, 2019 at 11:26:09PM -0700, Xing, Cedric wrote:
    > > > > From: Christopherson, Sean J
    > > > > Sent: Friday, May 31, 2019 4:32 PM
    > > > >
    > > > > +/**
    > > > > + * sgx_ioc_enclave_add_pages - handler for %SGX_IOC_ENCLAVE_ADD_PAGES
    > > > > + *
    > > > > + * @filep: open file to /dev/sgx
    > > > > + * @cmd: the command value
    > > > > + * @arg: pointer to an &sgx_enclave_add_page instance
    > > > > + *
    > > > > + * Add a range of pages to an uninitialized enclave (EADD), and
    > > > > +optionally
    > > > > + * extend the enclave's measurement with the contents of the page (EEXTEND).
    > > > > + * The range of pages must be virtually contiguous. The SECINFO and
    > > > > + * measurement maskare applied to all pages, i.e. pages with different
    > > > > + * properties must be added in separate calls.
    > > > > + *
    > > > > + * EADD and EEXTEND are done asynchronously via worker threads. A
    > > > > +successful
    > > > > + * sgx_ioc_enclave_add_page() only indicates the pages have been added
    > > > > +to the
    > > > > + * work queue, it does not guarantee adding the pages to the enclave
    > > > > +will
    > > > > + * succeed.
    > > > > + *
    > > > > + * Return:
    > > > > + * 0 on success,
    > > > > + * -errno otherwise
    > > > > + */
    > > > > +static long sgx_ioc_enclave_add_pages(struct file *filep, unsigned int cmd,
    > > > > + unsigned long arg)
    > > > > +{
    > > > > + struct sgx_enclave_add_pages *addp = (void *)arg;
    > > > > + struct sgx_encl *encl = filep->private_data;
    > > > > + struct sgx_secinfo secinfo;
    > > > > + unsigned int i;
    > > > > + int ret;
    > > > > +
    > > > > + if (copy_from_user(&secinfo, (void __user *)addp->secinfo,
    > > > > + sizeof(secinfo)))
    > > > > + return -EFAULT;
    > > > > +
    > > > > + for (i = 0, ret = 0; i < addp->nr_pages && !ret; i++) {
    > > > > + if (signal_pending(current))
    > > > > + return -ERESTARTSYS;
    > > >
    > > > If interrupted, how would user mode code know how many pages have been EADD'ed?
    > >
    > > Hmm, updating nr_pages would be fairly simple and shouldn't confuse
    > > userspace, e.g. as opposed to overloading the return value.
    >
    > Or maybe update @addr and @src as well? That would allow userspace to
    > re-invoke the ioctl() without having to modify the struct.

    If you're going to use -ERESTARTSYS, that's the way to go. -EINTR
    would be an alternative. A benefit of -ERESTARTSYS is that, with
    -EINTR, it wouldn't be that surprising for user code to simply fail to
    handle it.

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