Re: [RFC PATCH v4 2/4] x86/sgx: Implement support for MADV_WILLNEED

Jarkko Sakkinen
2023-02-07T23:28:41Z

On Fri, Jan 27, 2023 at 08:55:27PM -0800, Haitao Huang wrote:
> Support madvise(..., MADV_WILLNEED) by adding EPC pages with EAUG in
> the newly added fops->fadvise() callback implementation, sgx_fadvise().
>
> Change the return type and values of the sgx_encl_eaug_page function
> so that more specific error codes are returned for different treatment
> by the page fault handler and the fadvise callback.
> On any error, sgx_fadvise() will discontinue further operations
> and return as normal. The page fault handler allows a PF retried
> by returning VM_FAULT_NOPAGE in handling -EBUSY returned from
> sgx_encl_eaug_page.
>
> Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>
> ---
> arch/x86/kernel/cpu/sgx/driver.c | 74 ++++++++++++++++++++++++++++++++
> arch/x86/kernel/cpu/sgx/encl.c | 59 ++++++++++++++-----------
> arch/x86/kernel/cpu/sgx/encl.h | 4 +-
> 3 files changed, 111 insertions(+), 26 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/driver.c b/arch/x86/kernel/cpu/sgx/driver.c
> index aa9b8b868867..3a88daddc1a1 100644
> --- a/arch/x86/kernel/cpu/sgx/driver.c
> +++ b/arch/x86/kernel/cpu/sgx/driver.c
> @@ -2,6 +2,7 @@
> /* Copyright(c) 2016-20 Intel Corporation. */
>
> #include <linux/acpi.h>
> +#include <linux/fadvise.h>
> #include <linux/miscdevice.h>
> #include <linux/mman.h>
> #include <linux/security.h>
> @@ -9,6 +10,7 @@
> #include <asm/traps.h>
> #include "driver.h"
> #include "encl.h"
> +#include "encls.h"
>
> u64 sgx_attributes_reserved_mask;
> u64 sgx_xfrm_reserved_mask = ~0x3;
> @@ -97,10 +99,81 @@ static int sgx_mmap(struct file *file, struct vm_area_struct *vma)
> vma->vm_ops = &sgx_vm_ops;
> vma->vm_flags |= VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP | VM_IO;
> vma->vm_private_data = encl;
> + vma->vm_pgoff = PFN_DOWN(vma->vm_start - encl->base);
>
> return 0;
> }
>
> +/*
> + * Add new pages to the enclave sequentially with ENCLS[EAUG] for the WILLNEED advice.
> + * Only do this to existing VMAs in the same enclave and reject the request otherwise.
> + */
> +static int sgx_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
> +{
> + struct sgx_encl *encl = file->private_data;
> + unsigned long start = offset + encl->base;
> + struct vm_area_struct *vma = NULL;
> + unsigned long end = start + len;
> + unsigned long pos;
> + int ret = -EINVAL;
> +
> + if (!cpu_feature_enabled(X86_FEATURE_SGX2))
> + return -EINVAL;
> + /* Only support WILLNEED */
> + if (advice != POSIX_FADV_WILLNEED)
> + return -EINVAL;
> +
> + if (offset + len < offset)
> + return -EINVAL;
> + if (start < encl->base)
> + return -EINVAL;
> + if (end < start)
> + return -EINVAL;
> + if (end > encl->base + encl->size)
> + return -EINVAL;
> +
> + if (!test_bit(SGX_ENCL_INITIALIZED, &encl->flags))
> + return -EINVAL;
> +
> + mmap_read_lock(current->mm);
> +
> + vma = find_vma(current->mm, start);
> + if (!vma)
> + goto unlock;
> + if (vma->vm_private_data != encl)
> + goto unlock;
> +
> + pos = start;
> + if (pos < vma->vm_start || end > vma->vm_end) {
> + /* Don't allow any gaps */
> + goto unlock;
> + }
> +
> + /* Here: vm_start <= pos < end <= vm_end */
> + while (pos < end) {
> + if (xa_load(&encl->page_array, PFN_DOWN(pos)))
> + continue;
> + if (signal_pending(current)) {
> + if (pos == start)
> + ret = -ERESTARTSYS;
> + else
> + ret = -EINTR;
> + goto unlock;
> + }
> + ret = sgx_encl_eaug_page(vma, encl, pos);
> + /* It's OK to not finish */
> + if (ret)
> + break;
> + pos = pos + PAGE_SIZE;
> + cond_resched();
> + }
> + ret = 0;
> +
> +unlock:
> + mmap_read_unlock(current->mm);
> + return ret;
> +}
> +
> static unsigned long sgx_get_unmapped_area(struct file *file,
> unsigned long addr,
> unsigned long len,
> @@ -133,6 +206,7 @@ static const struct file_operations sgx_encl_fops = {
> .compat_ioctl = sgx_compat_ioctl,
> #endif
> .mmap = sgx_mmap,
> + .fadvise = sgx_fadvise,
> .get_unmapped_area = sgx_get_unmapped_area,
> };
>
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> index 0185c5ab48dd..592cfea4c9e4 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -299,20 +299,17 @@ struct sgx_encl_page *sgx_encl_load_page(struct sgx_encl *encl,
> }
>
> /**
> - * sgx_encl_eaug_page() - Dynamically add page to initialized enclave
> - * @vma: VMA obtained from fault info from where page is accessed
> - * @encl: enclave accessing the page
> - * @addr: address that triggered the page fault
> + * sgx_encl_eaug_page() - Dynamically add an EPC page to initialized enclave
> + * @vma: the VMA into which the page is to be added
> + * @encl: the enclave for which the page is to be added
> + * @addr: the start address of the page to be added
> *
> - * When an initialized enclave accesses a page with no backing EPC page
> - * on a SGX2 system then the EPC can be added dynamically via the SGX2
> - * ENCLS[EAUG] instruction.
> - *
> - * Returns: Appropriate vm_fault_t: VM_FAULT_NOPAGE when PTE was installed
> - * successfully, VM_FAULT_SIGBUS or VM_FAULT_OOM as error otherwise.
> + * Returns: 0 on EAUG success and PTE was installed successfully, -EBUSY for
> + * waiting on reclaimer to free EPC, -ENOMEM for out of RAM, -EFAULT for
> + * all other failures.
> */
> -vm_fault_t sgx_encl_eaug_page(struct vm_area_struct *vma,
> - struct sgx_encl *encl, unsigned long addr)
> +int sgx_encl_eaug_page(struct vm_area_struct *vma,
> + struct sgx_encl *encl, unsigned long addr)
> {
> vm_fault_t vmret = VM_FAULT_SIGBUS;
> struct sgx_pageinfo pginfo = {0};
> @@ -321,10 +318,10 @@ vm_fault_t sgx_encl_eaug_page(struct vm_area_struct *vma,
> struct sgx_va_page *va_page;
> unsigned long phys_addr;
> u64 secinfo_flags;
> - int ret;
> + int ret = -EFAULT;
>
> if (!test_bit(SGX_ENCL_INITIALIZED, &encl->flags))
> - return VM_FAULT_SIGBUS;
> + return -EFAULT;
>
> /*
> * Ignore internal permission checking for dynamically added pages.
> @@ -335,21 +332,21 @@ vm_fault_t sgx_encl_eaug_page(struct vm_area_struct *vma,
> secinfo_flags = SGX_SECINFO_R | SGX_SECINFO_W | SGX_SECINFO_X;
> encl_page = sgx_encl_page_alloc(encl, addr - encl->base, secinfo_flags);
> if (IS_ERR(encl_page))
> - return VM_FAULT_OOM;
> + return -ENOMEM;
>
> mutex_lock(&encl->lock);
>
> epc_page = sgx_alloc_epc_page(encl_page, false);
> if (IS_ERR(epc_page)) {
> if (PTR_ERR(epc_page) == -EBUSY)
> - vmret = VM_FAULT_NOPAGE;
> + ret = -EBUSY;
> goto err_out_unlock;
> }
>
> va_page = sgx_encl_grow(encl, false);
> if (IS_ERR(va_page)) {
> if (PTR_ERR(va_page) == -EBUSY)
> - vmret = VM_FAULT_NOPAGE;
> + ret = -EBUSY;
> goto err_out_epc;
> }
>
> @@ -362,16 +359,20 @@ vm_fault_t sgx_encl_eaug_page(struct vm_area_struct *vma,
> * If ret == -EBUSY then page was created in another flow while
> * running without encl->lock
> */
> - if (ret)
> + if (ret) {
> + ret = -EFAULT;
> goto err_out_shrink;
> + }
>
> pginfo.secs = (unsigned long)sgx_get_epc_virt_addr(encl->secs.epc_page);
> pginfo.addr = encl_page->desc & PAGE_MASK;
> pginfo.metadata = 0;
>
> ret = __eaug(&pginfo, sgx_get_epc_virt_addr(epc_page));
> - if (ret)
> + if (ret) {
> + ret = -EFAULT;
> goto err_out;
> + }
>
> encl_page->encl = encl;
> encl_page->epc_page = epc_page;
> @@ -388,10 +389,10 @@ vm_fault_t sgx_encl_eaug_page(struct vm_area_struct *vma,
> vmret = vmf_insert_pfn(vma, addr, PFN_DOWN(phys_addr));
> if (vmret != VM_FAULT_NOPAGE) {
> mutex_unlock(&encl->lock);
> - return VM_FAULT_SIGBUS;
> + return -EFAULT;
> }
> mutex_unlock(&encl->lock);
> - return VM_FAULT_NOPAGE;
> + return 0;
>
> err_out:
> xa_erase(&encl->page_array, PFN_DOWN(encl_page->desc));
> @@ -404,7 +405,7 @@ vm_fault_t sgx_encl_eaug_page(struct vm_area_struct *vma,
> mutex_unlock(&encl->lock);
> kfree(encl_page);
>
> - return vmret;
> + return ret;
> }
>
> static vm_fault_t sgx_vma_fault(struct vm_fault *vmf)
> @@ -434,8 +435,18 @@ static vm_fault_t sgx_vma_fault(struct vm_fault *vmf)
> * enclave that will be checked for right away.
> */
> if (cpu_feature_enabled(X86_FEATURE_SGX2) &&
> - (!xa_load(&encl->page_array, PFN_DOWN(addr))))
> - return sgx_encl_eaug_page(vma, encl, addr);
> + (!xa_load(&encl->page_array, PFN_DOWN(addr)))) {
> + switch (sgx_encl_eaug_page(vma, encl, addr)) {
> + case 0:
> + case -EBUSY:
> + return VM_FAULT_NOPAGE;
> + case -ENOMEM:
> + return VM_FAULT_OOM;
> + case -EFAULT:
> + default:
> + return VM_FAULT_SIGBUS;
> + }
> + }
>
> mutex_lock(&encl->lock);
>
> diff --git a/arch/x86/kernel/cpu/sgx/encl.h b/arch/x86/kernel/cpu/sgx/encl.h
> index 9f19b06c3ae3..e5a507871fa3 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.h
> +++ b/arch/x86/kernel/cpu/sgx/encl.h
> @@ -125,7 +125,7 @@ struct sgx_encl_page *sgx_encl_load_page(struct sgx_encl *encl,
> unsigned long addr);
> struct sgx_va_page *sgx_encl_grow(struct sgx_encl *encl, bool reclaim);
> void sgx_encl_shrink(struct sgx_encl *encl, struct sgx_va_page *va_page);
> -vm_fault_t sgx_encl_eaug_page(struct vm_area_struct *vma,
> - struct sgx_encl *encl, unsigned long addr);
> +int sgx_encl_eaug_page(struct vm_area_struct *vma,
> + struct sgx_encl *encl, unsigned long addr);
>
> #endif /* _X86_ENCL_H */
> --
> 2.25.1
>

Looks good to me!

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

BR, Jarkko