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    Subject[PATCH v34 09/24] x86/sgx: Add __sgx_alloc_epc_page() and sgx_free_epc_page()
    Date
    Add __sgx_alloc_epc_page(), which iterates through EPC sections and borrows
    a page structure that is not used by anyone else. When a page is no longer
    needed it must be released with sgx_free_epc_page(). This function
    implicitly calls ENCLS[EREMOVE], which will return the page to the
    uninitialized state (i.e. not required from caller part).

    Acked-by: Jethro Beekman <jethro@fortanix.com>
    Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
    Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
    Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
    ---
    arch/x86/kernel/cpu/sgx/main.c | 62 ++++++++++++++++++++++++++++++++++
    arch/x86/kernel/cpu/sgx/sgx.h | 3 ++
    2 files changed, 65 insertions(+)

    diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
    index c5831e3db14a..97c6895fb6c9 100644
    --- a/arch/x86/kernel/cpu/sgx/main.c
    +++ b/arch/x86/kernel/cpu/sgx/main.c
    @@ -83,6 +83,68 @@ static bool __init sgx_page_reclaimer_init(void)
    return true;
    }

    +static struct sgx_epc_page *__sgx_alloc_epc_page_from_section(struct sgx_epc_section *section)
    +{
    + struct sgx_epc_page *page;
    +
    + if (list_empty(&section->page_list))
    + return NULL;
    +
    + page = list_first_entry(&section->page_list, struct sgx_epc_page, list);
    + list_del_init(&page->list);
    +
    + return page;
    +}
    +
    +/**
    + * __sgx_alloc_epc_page() - Allocate an EPC page
    + *
    + * Iterate through EPC sections and borrow a free EPC page to the caller. When a
    + * page is no longer needed it must be released with sgx_free_epc_page().
    + *
    + * Return:
    + * an EPC page,
    + * -errno on error
    + */
    +struct sgx_epc_page *__sgx_alloc_epc_page(void)
    +{
    + struct sgx_epc_section *section;
    + struct sgx_epc_page *page;
    + int i;
    +
    + for (i = 0; i < sgx_nr_epc_sections; i++) {
    + section = &sgx_epc_sections[i];
    + spin_lock(&section->lock);
    + page = __sgx_alloc_epc_page_from_section(section);
    + spin_unlock(&section->lock);
    +
    + if (page)
    + return page;
    + }
    +
    + return ERR_PTR(-ENOMEM);
    +}
    +
    +/**
    + * sgx_free_epc_page() - Free an EPC page
    + * @page: an EPC page
    + *
    + * Call EREMOVE for an EPC page and insert it back to the list of free pages.
    + */
    +void sgx_free_epc_page(struct sgx_epc_page *page)
    +{
    + struct sgx_epc_section *section = sgx_get_epc_section(page);
    + int ret;
    +
    + ret = __eremove(sgx_get_epc_addr(page));
    + if (WARN_ONCE(ret, "EREMOVE returned %d (0x%x)", ret, ret))
    + return;
    +
    + spin_lock(&section->lock);
    + list_add_tail(&page->list, &section->page_list);
    + spin_unlock(&section->lock);
    +}
    +
    static void __init sgx_free_epc_section(struct sgx_epc_section *section)
    {
    struct sgx_epc_page *page;
    diff --git a/arch/x86/kernel/cpu/sgx/sgx.h b/arch/x86/kernel/cpu/sgx/sgx.h
    index dff4f5f16d09..fce756c3434b 100644
    --- a/arch/x86/kernel/cpu/sgx/sgx.h
    +++ b/arch/x86/kernel/cpu/sgx/sgx.h
    @@ -49,4 +49,7 @@ static inline void *sgx_get_epc_addr(struct sgx_epc_page *page)
    return section->va + (page->desc & PAGE_MASK) - section->pa;
    }

    +struct sgx_epc_page *__sgx_alloc_epc_page(void);
    +void sgx_free_epc_page(struct sgx_epc_page *page);
    +
    #endif /* _X86_SGX_H */
    --
    2.25.1
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