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    SubjectRe: [PATCH Part2 v6 14/49] crypto: ccp: Handle the legacy TMR allocation when SNP is enabled
    On Mon, Jun 20, 2022 at 5:05 PM Ashish Kalra <Ashish.Kalra@amd.com> wrote:
    >
    > From: Brijesh Singh <brijesh.singh@amd.com>
    >
    > The behavior and requirement for the SEV-legacy command is altered when
    > the SNP firmware is in the INIT state. See SEV-SNP firmware specification
    > for more details.
    >
    > Allocate the Trusted Memory Region (TMR) as a 2mb sized/aligned region
    > when SNP is enabled to satify new requirements for the SNP. Continue

    satisfy

    > allocating a 1mb region for !SNP configuration.
    >
    > While at it, provide API that can be used by others to allocate a page
    > that can be used by the firmware. The immediate user for this API will
    > be the KVM driver. The KVM driver to need to allocate a firmware context
    > page during the guest creation. The context page need to be updated
    > by the firmware. See the SEV-SNP specification for further details.
    >
    > Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
    > ---
    > drivers/crypto/ccp/sev-dev.c | 173 +++++++++++++++++++++++++++++++++--
    > include/linux/psp-sev.h | 11 +++
    > 2 files changed, 178 insertions(+), 6 deletions(-)
    >
    > diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
    > index 35d76333e120..0dbd99f29b25 100644
    > --- a/drivers/crypto/ccp/sev-dev.c
    > +++ b/drivers/crypto/ccp/sev-dev.c
    > @@ -79,6 +79,14 @@ static void *sev_es_tmr;
    > #define NV_LENGTH (32 * 1024)
    > static void *sev_init_ex_buffer;
    >
    > +/* When SEV-SNP is enabled the TMR needs to be 2MB aligned and 2MB size. */
    > +#define SEV_SNP_ES_TMR_SIZE (2 * 1024 * 1024)
    > +
    > +static size_t sev_es_tmr_size = SEV_ES_TMR_SIZE;

    Why not keep all this TMR stuff together near the SEV_ES_TMR_SIZE define?

    > +
    > +static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret);
    > +static int sev_do_cmd(int cmd, void *data, int *psp_ret);
    > +
    > static inline bool sev_version_greater_or_equal(u8 maj, u8 min)
    > {
    > struct sev_device *sev = psp_master->sev_data;
    > @@ -177,11 +185,161 @@ static int sev_cmd_buffer_len(int cmd)
    > return 0;
    > }
    >
    > +static void snp_leak_pages(unsigned long pfn, unsigned int npages)
    > +{
    > + WARN(1, "psc failed, pfn 0x%lx pages %d (leaking)\n", pfn, npages);
    > + while (npages--) {
    > + memory_failure(pfn, 0);
    > + dump_rmpentry(pfn);
    > + pfn++;
    > + }
    > +}
    > +
    > +static int snp_reclaim_pages(unsigned long pfn, unsigned int npages, bool locked)
    > +{
    > + struct sev_data_snp_page_reclaim data;
    > + int ret, err, i, n = 0;
    > +
    > + for (i = 0; i < npages; i++) {

    What about setting |n| here too, also the other increments.

    for (i = 0, n = 0; i < npages; i++, n++, pfn++)

    > + memset(&data, 0, sizeof(data));
    > + data.paddr = pfn << PAGE_SHIFT;
    > +
    > + if (locked)
    > + ret = __sev_do_cmd_locked(SEV_CMD_SNP_PAGE_RECLAIM, &data, &err);
    > + else
    > + ret = sev_do_cmd(SEV_CMD_SNP_PAGE_RECLAIM, &data, &err);

    Can we change `sev_cmd_mutex` to some sort of nesting lock type? That
    could clean up this if (locked) code.

    > + if (ret)
    > + goto cleanup;
    > +
    > + ret = rmp_make_shared(pfn, PG_LEVEL_4K);
    > + if (ret)
    > + goto cleanup;
    > +
    > + pfn++;
    > + n++;
    > + }
    > +
    > + return 0;
    > +
    > +cleanup:
    > + /*
    > + * If failed to reclaim the page then page is no longer safe to
    > + * be released, leak it.
    > + */
    > + snp_leak_pages(pfn, npages - n);
    > + return ret;
    > +}
    > +
    > +static inline int rmp_make_firmware(unsigned long pfn, int level)
    > +{
    > + return rmp_make_private(pfn, 0, level, 0, true);
    > +}
    > +
    > +static int snp_set_rmp_state(unsigned long paddr, unsigned int npages, bool to_fw, bool locked,
    > + bool need_reclaim)

    This function can do a lot and when I read the call sites its hard to
    see what its doing since we have a combination of arguments which tell
    us what behavior is happening, some of which are not valid (ex: to_fw
    == true and need_reclaim == true is an invalid argument combination).
    Also this for loop over |npages| is duplicated from
    snp_reclaim_pages(). One improvement here is that on the current
    snp_reclaim_pages() if we fail to reclaim a page we assume we cannot
    reclaim the next pages, this may cause us to snp_leak_pages() more
    pages than we actually need too.

    What about something like this?

    static snp_leak_page(u64 pfn, enum pg_level level)
    {
    memory_failure(pfn, 0);
    dump_rmpentry(pfn);
    }

    static int snp_reclaim_page(u64 pfn, enum pg_level level)
    {
    int ret;
    struct sev_data_snp_page_reclaim data;

    ret = sev_do_cmd(SEV_CMD_SNP_PAGE_RECLAIM, &data, &err);
    if (ret)
    goto cleanup;

    ret = rmp_make_shared(pfn, level);
    if (ret)
    goto cleanup;

    return 0;

    cleanup:
    snp_leak_page(pfn, level)
    }

    typedef int (*rmp_state_change_func) (u64 pfn, enum pg_level level);

    static int snp_set_rmp_state(unsigned long paddr, unsigned int npages,
    rmp_state_change_func state_change, rmp_state_change_func cleanup)
    {
    struct sev_data_snp_page_reclaim data;
    int ret, err, i, n = 0;

    for (i = 0, n = 0; i < npages; i++, n++, pfn++) {
    ret = state_change(pfn, PG_LEVEL_4K)
    if (ret)
    goto cleanup;
    }

    return 0;

    cleanup:
    for (; i>= 0; i--, n--, pfn--) {
    cleanup(pfn, PG_LEVEL_4K);
    }

    return ret;
    }

    Then inside of __snp_alloc_firmware_pages():

    snp_set_rmp_state(paddr, npages, rmp_make_firmware, snp_reclaim_page);

    And inside of __snp_free_firmware_pages():

    snp_set_rmp_state(paddr, npages, snp_reclaim_page, snp_leak_page);

    Just a suggestion feel free to ignore. The readability comment could
    be addressed much less invasively by just making separate functions
    for each valid combination of arguments here. Like
    snp_set_rmp_fw_state(), snp_set_rmp_shared_state(),
    snp_set_rmp_release_state() or something.

    > +{
    > + unsigned long pfn = __sme_clr(paddr) >> PAGE_SHIFT; /* Cbit maybe set in the paddr */
    > + int rc, n = 0, i;
    > +
    > + for (i = 0; i < npages; i++) {
    > + if (to_fw)
    > + rc = rmp_make_firmware(pfn, PG_LEVEL_4K);
    > + else
    > + rc = need_reclaim ? snp_reclaim_pages(pfn, 1, locked) :
    > + rmp_make_shared(pfn, PG_LEVEL_4K);
    > + if (rc)
    > + goto cleanup;
    > +
    > + pfn++;
    > + n++;
    > + }
    > +
    > + return 0;
    > +
    > +cleanup:
    > + /* Try unrolling the firmware state changes */
    > + if (to_fw) {
    > + /*
    > + * Reclaim the pages which were already changed to the
    > + * firmware state.
    > + */
    > + snp_reclaim_pages(paddr >> PAGE_SHIFT, n, locked);
    > +
    > + return rc;
    > + }
    > +
    > + /*
    > + * If failed to change the page state to shared, then its not safe
    > + * to release the page back to the system, leak it.
    > + */
    > + snp_leak_pages(pfn, npages - n);
    > +
    > + return rc;
    > +}
    > +
    > +static struct page *__snp_alloc_firmware_pages(gfp_t gfp_mask, int order, bool locked)
    > +{
    > + unsigned long npages = 1ul << order, paddr;
    > + struct sev_device *sev;
    > + struct page *page;
    > +
    > + if (!psp_master || !psp_master->sev_data)
    > + return NULL;
    > +
    > + page = alloc_pages(gfp_mask, order);
    > + if (!page)
    > + return NULL;
    > +
    > + /* If SEV-SNP is initialized then add the page in RMP table. */
    > + sev = psp_master->sev_data;
    > + if (!sev->snp_inited)
    > + return page;
    > +
    > + paddr = __pa((unsigned long)page_address(page));
    > + if (snp_set_rmp_state(paddr, npages, true, locked, false))
    > + return NULL;

    So what about the case where snp_set_rmp_state() fails but we were
    able to reclaim all the pages? Should we be able to signal that to
    callers so that we could free |page| here? But given this is an error
    path already maybe we can optimize this in a follow up series.

    > +
    > + return page;
    > +}
    > +
    > +void *snp_alloc_firmware_page(gfp_t gfp_mask)
    > +{
    > + struct page *page;
    > +
    > + page = __snp_alloc_firmware_pages(gfp_mask, 0, false);
    > +
    > + return page ? page_address(page) : NULL;
    > +}
    > +EXPORT_SYMBOL_GPL(snp_alloc_firmware_page);
    > +
    > +static void __snp_free_firmware_pages(struct page *page, int order, bool locked)
    > +{
    > + unsigned long paddr, npages = 1ul << order;
    > +
    > + if (!page)
    > + return;
    > +
    > + paddr = __pa((unsigned long)page_address(page));
    > + if (snp_set_rmp_state(paddr, npages, false, locked, true))
    > + return;

    Here we may be able to free some of |page| depending how where inside
    of snp_set_rmp_state() we failed. But again given this is an error
    path already maybe we can optimize this in a follow up series.



    > +
    > + __free_pages(page, order);
    > +}
    > +
    > +void snp_free_firmware_page(void *addr)
    > +{
    > + if (!addr)
    > + return;
    > +
    > + __snp_free_firmware_pages(virt_to_page(addr), 0, false);
    > +}
    > +EXPORT_SYMBOL(snp_free_firmware_page);
    > +
    > static void *sev_fw_alloc(unsigned long len)
    > {
    > struct page *page;
    >
    > - page = alloc_pages(GFP_KERNEL, get_order(len));
    > + page = __snp_alloc_firmware_pages(GFP_KERNEL, get_order(len), false);
    > if (!page)
    > return NULL;
    >
    > @@ -393,7 +551,7 @@ static int __sev_init_locked(int *error)
    > data.tmr_address = __pa(sev_es_tmr);
    >
    > data.flags |= SEV_INIT_FLAGS_SEV_ES;
    > - data.tmr_len = SEV_ES_TMR_SIZE;
    > + data.tmr_len = sev_es_tmr_size;
    > }
    >
    > return __sev_do_cmd_locked(SEV_CMD_INIT, &data, error);
    > @@ -421,7 +579,7 @@ static int __sev_init_ex_locked(int *error)
    > data.tmr_address = __pa(sev_es_tmr);
    >
    > data.flags |= SEV_INIT_FLAGS_SEV_ES;
    > - data.tmr_len = SEV_ES_TMR_SIZE;
    > + data.tmr_len = sev_es_tmr_size;
    > }
    >
    > return __sev_do_cmd_locked(SEV_CMD_INIT_EX, &data, error);
    > @@ -818,6 +976,8 @@ static int __sev_snp_init_locked(int *error)
    > sev->snp_inited = true;
    > dev_dbg(sev->dev, "SEV-SNP firmware initialized\n");
    >
    > + sev_es_tmr_size = SEV_SNP_ES_TMR_SIZE;
    > +
    > return rc;
    > }
    >
    > @@ -1341,8 +1501,9 @@ static void sev_firmware_shutdown(struct sev_device *sev)
    > /* The TMR area was encrypted, flush it from the cache */
    > wbinvd_on_all_cpus();
    >
    > - free_pages((unsigned long)sev_es_tmr,
    > - get_order(SEV_ES_TMR_SIZE));
    > + __snp_free_firmware_pages(virt_to_page(sev_es_tmr),
    > + get_order(sev_es_tmr_size),
    > + false);
    > sev_es_tmr = NULL;
    > }
    >
    > @@ -1430,7 +1591,7 @@ void sev_pci_init(void)
    > }
    >
    > /* Obtain the TMR memory area for SEV-ES use */
    > - sev_es_tmr = sev_fw_alloc(SEV_ES_TMR_SIZE);
    > + sev_es_tmr = sev_fw_alloc(sev_es_tmr_size);
    > if (!sev_es_tmr)
    > dev_warn(sev->dev,
    > "SEV: TMR allocation failed, SEV-ES support unavailable\n");
    > diff --git a/include/linux/psp-sev.h b/include/linux/psp-sev.h
    > index 9f921d221b75..a3bb792bb842 100644
    > --- a/include/linux/psp-sev.h
    > +++ b/include/linux/psp-sev.h
    > @@ -12,6 +12,8 @@
    > #ifndef __PSP_SEV_H__
    > #define __PSP_SEV_H__
    >
    > +#include <linux/sev.h>
    > +
    > #include <uapi/linux/psp-sev.h>
    >
    > #ifdef CONFIG_X86
    > @@ -940,6 +942,8 @@ int snp_guest_page_reclaim(struct sev_data_snp_page_reclaim *data, int *error);
    > int snp_guest_dbg_decrypt(struct sev_data_snp_dbg *data, int *error);
    >
    > void *psp_copy_user_blob(u64 uaddr, u32 len);
    > +void *snp_alloc_firmware_page(gfp_t mask);
    > +void snp_free_firmware_page(void *addr);
    >
    > #else /* !CONFIG_CRYPTO_DEV_SP_PSP */
    >
    > @@ -981,6 +985,13 @@ static inline int snp_guest_dbg_decrypt(struct sev_data_snp_dbg *data, int *erro
    > return -ENODEV;
    > }
    >
    > +static inline void *snp_alloc_firmware_page(gfp_t mask)
    > +{
    > + return NULL;
    > +}
    > +
    > +static inline void snp_free_firmware_page(void *addr) { }
    > +
    > #endif /* CONFIG_CRYPTO_DEV_SP_PSP */
    >
    > #endif /* __PSP_SEV_H__ */
    > --
    > 2.25.1
    >

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