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    SubjectRe: [PATCH v22 09/24] x86/sgx: Add functions to allocate and free EPC pages
    On Tue, Sep 03, 2019 at 05:26:40PM +0300, Jarkko Sakkinen wrote:
    > Add functions for grabbing EPC pages into use:
    >
    > * sgx_alloc_page(): Iterate the EPC sections and return the first free
    > page, or ERR_PTR(-ENOMEM) when no free pages are available.
    > * __sgx_free_page(): Return the page into uninitialized state and move
    > it back to the corresponding EPC section structure. Issues WARN()
    > when EREMOVE fails.
    > * sgx_free_page(): Return the page into uninitialized state and move
    > it back to the corresponding EPC section structure. Returns
    > ENCLS[EREMOVE] error code back to the caller.
    >
    > [1] Intel SDM: 40.3 INTEL® SGX SYSTEM LEAF FUNCTION REFERENCE
    >
    > Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
    > Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
    > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
    > ---
    > arch/x86/kernel/cpu/sgx/main.c | 90 ++++++++++++++++++++++++++++++++++
    > arch/x86/kernel/cpu/sgx/sgx.h | 4 ++
    > 2 files changed, 94 insertions(+)
    >
    > diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
    > index e2317f6e4374..6b4727df72ca 100644
    > --- a/arch/x86/kernel/cpu/sgx/main.c
    > +++ b/arch/x86/kernel/cpu/sgx/main.c
    > @@ -9,6 +9,7 @@
    > #include <linux/sched/signal.h>
    > #include <linux/slab.h>
    > #include "arch.h"
    > +#include "encls.h"
    > #include "sgx.h"
    >
    > struct sgx_epc_section sgx_epc_sections[SGX_MAX_EPC_SECTIONS];
    > @@ -16,6 +17,95 @@ EXPORT_SYMBOL_GPL(sgx_epc_sections);
    >
    > int sgx_nr_epc_sections;
    >
    > +static struct sgx_epc_page *sgx_section_get_page(

    That fits into 80 cols (oh well, 81) and even if not, a trailing opening
    arg brace is ugly.

    > + struct sgx_epc_section *section)
    > +{
    > + struct sgx_epc_page *page;
    > +
    > + if (!section->free_cnt)
    > + return NULL;
    > +
    > + page = list_first_entry(&section->page_list,
    > + struct sgx_epc_page, list);

    That fits in 80-cols too. Why break it?

    > + list_del_init(&page->list);
    > + section->free_cnt--;
    > + return page;
    > +}
    > +
    > +/**
    > + * sgx_alloc_page - Allocate an EPC page
    > + *
    > + * Try to grab a page from the free EPC page list.
    > + *
    > + * Return:
    > + * a pointer to a &struct sgx_epc_page instance,
    > + * -errno on error
    > + */
    > +struct sgx_epc_page *sgx_alloc_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_section_get_page(section);
    > + spin_unlock(&section->lock);
    > +
    > + if (page)
    > + return page;
    > + }
    > +
    > + return ERR_PTR(-ENOMEM);
    > +}
    > +EXPORT_SYMBOL_GPL(sgx_alloc_page);

    That export gets removed later too. But you know already...

    > +
    > +/**
    > + * __sgx_free_page - Free an EPC page
    > + * @page: pointer a previously allocated EPC page
    > + *
    > + * EREMOVE an EPC page and insert it back to the list of free pages.
    > + *
    > + * Return:
    > + * 0 on success
    > + * SGX error code if EREMOVE fails
    > + */
    > +int __sgx_free_page(struct sgx_epc_page *page)
    > +{
    > + struct sgx_epc_section *section = sgx_epc_section(page);
    > + int ret;

    Shouldn't you be grabbing the lock here already?

    Or nothing can happen to that page from another thread after you
    ENCLS[EREMOVE] it and before it is added to the ->page_list of the
    section?

    > +
    > + ret = __eremove(sgx_epc_addr(page));
    > + if (ret)
    > + return ret;
    > +
    > + spin_lock(&section->lock);
    > + list_add_tail(&page->list, &section->page_list);
    > + section->free_cnt++;
    > + spin_unlock(&section->lock);
    > +
    > + return 0;
    > +}
    > +EXPORT_SYMBOL_GPL(__sgx_free_page);
    > +
    > +/**
    > + * sgx_free_page - Free an EPC page and WARN on failure
    > + * @page: pointer to a previously allocated EPC page
    > + *
    > + * EREMOVE an EPC page and insert it back to the list of free pages, and WARN
    > + * if EREMOVE fails. For use when the call site cannot (or chooses not to)
    > + * handle failure, i.e. the page is leaked on failure.
    > + */
    > +void sgx_free_page(struct sgx_epc_page *page)
    > +{
    > + int ret;
    > +
    > + ret = __sgx_free_page(page);
    > + WARN(ret > 0, "sgx: EREMOVE returned %d (0x%x)", ret, ret);

    That will potentially flood dmesg. Why are we even accommodating such
    callers? They either handle the error or they don't get to alloc EPC
    pages. There's also __must_check with which you can enforce the error
    code checking or we simply don't allow not handling failure. Fullstop.

    Thx.

    --
    Regards/Gruss,
    Boris.

    https://people.kernel.org/tglx/notes-about-netiquette

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