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SubjectRe: [PATCH v5] x86: Remove unnecessary kmap() from sgx_ioc_enclave_init()
On Fri, Mar 05, 2021 at 04:20:58PM -0800, 'Ira Weiny' wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> kmap is inefficient and we are trying to reduce the usage in the kernel.
> There is no readily apparent reason why initp_page needs to be allocated
> and kmap'ed() but sigstruct needs to be page aligned and token
> 512 byte aligned.

Friendly ping, maybe I missed a response?
Ira

>
> kmalloc() can give us this alignment but we need to allocate PAGE_SIZE
> bytes to do so. Rather than change this kmap() to kmap_local_page() use
> kmalloc() instead.
>
> Remove the alloc_page()/kmap() and replace with kmalloc(PAGE_SIZE, ...)
> to get a page aligned kernel address to use.
>
> In addition add a comment to document the alignment requirements so that
> others like myself don't attempt to 'fix' this again.
>
> Cc: Sean Christopherson <seanjc@google.com>
> Cc: Jethro Beekman <jethro@fortanix.com>
> Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
> Acked-by: Dave Hansen <dave.hansen@intel.com>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
>
> ---
> 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.weiny@intel.com/
> [2] https://lore.kernel.org/lkml/20210202013725.3514671-1-ira.weiny@intel.com/
> [3] https://lore.kernel.org/lkml/20210205050850.GC5033@iweiny-DESK2.sc.intel.com/#t
> [4] https://lore.kernel.org/lkml/YCBY02iEKLVyj7Ix@kernel.org/
>
> ---
> arch/x86/kernel/cpu/sgx/ioctl.c | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> index 90a5caf76939..38e540de5e2a 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 +614,14 @@ 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 boundry and token on a 512 byte boundry
> + * kmalloc() gives us 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 +647,7 @@ 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
>

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