[PATCH] x86/sgx: Remove unnecessary kmap() from sgx_ioc_enclave_init()

[ira . weiny]

From: Ira Weiny <ira.we...@intel.com>

kmap is inefficient and is being replaced by kmap_local_page(), if
possible.

That said, there is no readily apparent reason why initp_page needs to
be allocated and kmap'ed() except that 'sigstruct' needs to be page
aligned and 'token' 512 byte aligned.

Rather than change this kmap() to kmap_local_page() use kmalloc()
instead because kmalloc() can gives this alignment when allocating
PAGE_SIZE bytes.

Remove the alloc_page()/kmap() and replace with kmalloc(PAGE_SIZE, ...)
to get a page aligned kernel address.

In addition add a comment to document the alignment requirements so that
others don't attempt to 'fix' this again.

Cc: Sean Christopherson <sea...@google.com>
Cc: Jethro Beekman <jet...@fortanix.com>
Cc: Jarkko Sakkinen <jar...@kernel.org>
Cc: Dave Hansen <dave.han...@intel.com>
Signed-off-by: Ira Weiny <ira.we...@intel.com>

---
Changes from v5[5]:
        From Boris
                Clean up commit msg and comment

Changes from v4[4]:
        Add Ack and Reviews
        Send to the correct maintainers

Changes from v3[3]:
        Remove BUILD_BUG_ONs

Changes from v2[2]:
        When allocating a power of 2 size kmalloc() now guarantees the
        alignment of the respective size.  So go back to using kmalloc() but
        with a PAGE_SIZE allocation to get the alignment.  This also follows
        the pattern in sgx_ioc_enclave_create()

Changes from v1[1]:
        Use page_address() instead of kcmalloc() to ensure sigstruct is
        page aligned
        Use BUILD_BUG_ON to ensure token and sigstruct don't collide.

[1] https://lore.kernel.org/lkml/20210129001459.1538805-1-ira.we...@intel.com/
[2] https://lore.kernel.org/lkml/20210202013725.3514671-1-ira.we...@intel.com/
[3] 
https://lore.kernel.org/lkml/20210205050850.gc5...@iweiny-desk2.sc.intel.com/#t
[4] https://lore.kernel.org/lkml/ycby02ieklvyj...@kernel.org/
[5] https://lore.kernel.org/lkml/20210306002058.303796-1-ira.we...@intel.com/
---
 arch/x86/kernel/cpu/sgx/ioctl.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
index 90a5caf76939..2e10367ea66c 100644
--- a/arch/x86/kernel/cpu/sgx/ioctl.c
+++ b/arch/x86/kernel/cpu/sgx/ioctl.c
@@ -604,7 +604,6 @@ static long sgx_ioc_enclave_init(struct sgx_encl *encl, 
void __user *arg)
 {
        struct sgx_sigstruct *sigstruct;
        struct sgx_enclave_init init_arg;
-       struct page *initp_page;
        void *token;
        int ret;
 
@@ -615,11 +614,15 @@ static long sgx_ioc_enclave_init(struct sgx_encl *encl, 
void __user *arg)
        if (copy_from_user(&init_arg, arg, sizeof(init_arg)))
                return -EFAULT;
 
-       initp_page = alloc_page(GFP_KERNEL);
-       if (!initp_page)
+       /*
+        * 'sigstruct' must be on a page boundary and 'token' on a 512 byte
+        * boundary.  kmalloc() will give this alignment when allocating
+        * PAGE_SIZE bytes.
+        */
+       sigstruct = kmalloc(PAGE_SIZE, GFP_KERNEL);
+       if (!sigstruct)
                return -ENOMEM;
 
-       sigstruct = kmap(initp_page);
        token = (void *)((unsigned long)sigstruct + PAGE_SIZE / 2);
        memset(token, 0, SGX_LAUNCH_TOKEN_SIZE);
 
@@ -645,8 +648,7 @@ static long sgx_ioc_enclave_init(struct sgx_encl *encl, 
void __user *arg)
        ret = sgx_encl_init(encl, sigstruct, token);
 
 out:
-       kunmap(initp_page);
-       __free_page(initp_page);
+       kfree(sigstruct);
        return ret;
 }
 
-- 
2.28.0.rc0.12.gb6a658bd00c9