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

[Jarkko Sakkinen <jarkko@kernel.org>]

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