Re: [PATCH RFC v8 24/56] crypto: ccp: Handle the legacy TMR allocation when SNP is enabled

[Zhi Wang]

On Mon, 20 Feb 2023 12:38:15 -0600
Michael Roth <michael.roth@xxxxxxx> wrote:

> From: Brijesh Singh <brijesh.singh@xxxxxxx>
> 
> 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 satisfy new requirements for the SNP. Continue
> 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.
> 
> Co-developed-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
> ---
>  drivers/crypto/ccp/sev-dev.c | 148 +++++++++++++++++++++++++++++++++--
>  include/linux/psp-sev.h      |   9 +++
>  2 files changed, 149 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/crypto/ccp/sev-dev.c b/drivers/crypto/ccp/sev-dev.c
> index eca4e59b0f44..4c12e98a1219 100644
> --- a/drivers/crypto/ccp/sev-dev.c
> +++ b/drivers/crypto/ccp/sev-dev.c
> @@ -94,6 +94,13 @@ static void *sev_init_ex_buffer;
>   */
>  struct sev_data_range_list *snp_range_list;
>  
> +/* When SEV-SNP is enabled the TMR needs to be 2MB aligned and 2MB size. */
> +#define SEV_SNP_ES_TMR_SIZE	(2 * 1024 * 1024)

It would be better to re-use the kernel size definition macros. E.g. SZ_2MB.

> +
> +static size_t sev_es_tmr_size = SEV_ES_TMR_SIZE;
> +
> +static int __sev_do_cmd_locked(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;
> @@ -216,11 +223,134 @@ void snp_mark_pages_offline(unsigned long pfn, unsigned int npages)
>  }
>  EXPORT_SYMBOL_GPL(snp_mark_pages_offline);
>  
> +static int snp_reclaim_pages(unsigned long paddr, unsigned int npages, bool locked)
> +{
> +	/* Cbit maybe set in the paddr */

This is confusing.

I suppose C-bit is treated as a attribute of PTE in the kernel not part of the
PA. It means only a PTE might carry a C-bit. 

The paddr is from __pa(page_address()). It is not extracted from a PTE. Thus, the
return from them should never have a C-bit.

BTW: Wouldn't it be better to have pfn as input param instead of paddr?

The caller has struct page, calling snp_reclaim_pages(page_to_pfn(page), xxxxx)
would be much clearer than the current conversion:
page_address() (struct page is converted to VA), __pa() (VA is converted to PA)
in the caller and then PA is converted to pfn here.

> +	unsigned long pfn = __sme_clr(paddr) >> PAGE_SHIFT;
> +	int ret, err, i, n = 0;
> +

should be unsigned int i, n; as the input param npage is unsigned int.

> +	if (!pfn_valid(pfn)) {
> +		pr_err("%s: Invalid PFN %lx\n", __func__, pfn);
> +		return 0;
> +	}
> +
> +	for (i = 0; i < npages; i++, pfn++, n++) {
> +		paddr = pfn << PAGE_SHIFT;
> +
> +		if (locked)
> +			ret = __sev_do_cmd_locked(SEV_CMD_SNP_PAGE_RECLAIM, &paddr, &err);
> +		else
> +			ret = sev_do_cmd(SEV_CMD_SNP_PAGE_RECLAIM, &paddr, &err);
> +
> +		if (ret)
> +			goto cleanup;
> +
> +		ret = rmp_make_shared(pfn, PG_LEVEL_4K);
> +		if (ret)
> +			goto cleanup;
> +	}
> +
> +	return 0;
> +
> +cleanup:
> +	/*
> +	 * If failed to reclaim the page then page is no longer safe to
> +	 * be release back to the system, leak it.
> +	 */
> +	snp_mark_pages_offline(pfn, npages - n);
> +	return ret;
> +}
> +
> +static int rmp_mark_pages_firmware(unsigned long paddr, unsigned int npages, bool locked)

The same comment as above. Better take pfn or page instead of paddr with
redundant conversions.

> +{
> +	/* Cbit maybe set in the paddr */
> +	unsigned long pfn = __sme_clr(paddr) >> PAGE_SHIFT;
> +	int rc, n = 0, i;
> +
> +	for (i = 0; i < npages; i++, n++, pfn++) {
> +		rc = rmp_make_private(pfn, 0, PG_LEVEL_4K, 0, true);
> +		if (rc)
> +			goto cleanup;
> +	}
> +
> +	return 0;
> +
> +cleanup:
> +	/*
> +	 * Try unrolling the firmware state changes by
> +	 * reclaiming the pages which were already changed to the
> +	 * firmware state.
> +	 */
> +	snp_reclaim_pages(paddr, n, locked);
> +
> +	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_initialized)
> +		return page;
> +
> +	paddr = __pa((unsigned long)page_address(page));
> +	if (rmp_mark_pages_firmware(paddr, npages, locked))
> +		return NULL;
> +
> +	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)
> +{
> +	struct sev_device *sev = psp_master->sev_data;
> +	unsigned long paddr, npages = 1ul << order;
> +
> +	if (!page)
> +		return;
> +
> +	paddr = __pa((unsigned long)page_address(page));
> +	if (sev->snp_initialized &&
> +	    snp_reclaim_pages(paddr, npages, locked))
> +		return;
> +
> +	__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_GPL(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;
>  
> @@ -468,7 +598,7 @@ 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);
> @@ -491,7 +621,7 @@ 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);
> @@ -982,6 +1112,8 @@ static int __sev_snp_init_locked(int *error)
>  	sev->snp_initialized = true;
>  	dev_dbg(sev->dev, "SEV-SNP firmware initialized\n");
>  
> +	sev_es_tmr_size = SEV_SNP_ES_TMR_SIZE;
> +
>  	return rc;
>  }
>  
> @@ -1499,8 +1631,9 @@ 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;
>  	}
>  
> @@ -1511,8 +1644,7 @@ static void sev_firmware_shutdown(struct sev_device *sev)
>  	}
>  
>  	if (snp_range_list) {
> -		free_pages((unsigned long)snp_range_list,
> -			   get_order(PAGE_SIZE));
> +		snp_free_firmware_page(snp_range_list);
>  		snp_range_list = NULL;
>  	}
>  
> @@ -1593,7 +1725,7 @@ 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 8edf5c548fbf..d19744807471 100644
> --- a/include/linux/psp-sev.h
> +++ b/include/linux/psp-sev.h
> @@ -922,6 +922,8 @@ int sev_guest_decommission(struct sev_data_decommission *data, int *error);
>  int sev_do_cmd(int cmd, void *data, int *psp_ret);
>  
>  void *psp_copy_user_blob(u64 uaddr, u32 len);
> +void *snp_alloc_firmware_page(gfp_t mask);
> +void snp_free_firmware_page(void *addr);
>  
>  /**
>   * sev_mark_pages_offline - insert non-reclaimed firmware/guest pages
> @@ -959,6 +961,13 @@ static inline void *psp_copy_user_blob(u64 __user uaddr, u32 len) { return ERR_P
>  
>  void snp_mark_pages_offline(unsigned long pfn, unsigned int npages) {}
>  
> +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__ */