linux-kernel - Re: [PATCH] x86/sgx: Replace kmap/kunmap

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Message-ID: <Y0BEV+Xgkrln8xoh@iweiny-desk3>
Date:   Fri, 7 Oct 2022 08:23:03 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Kristen Carlson Accardi <kristen@...ux.intel.com>
CC:     <linux-kernel@...r.kernel.org>, <linux-sgx@...r.kernel.org>,
        "Jarkko Sakkinen" <jarkko@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86/sgx: Replace kmap/kunmap_atomic calls

On Thu, Sep 29, 2022 at 09:06:46AM -0700, Kristen Carlson Accardi wrote:
> It is not necessary to disable page faults or preemption when
> using kmap calls, so replace kmap_atomic() and kunmap_atomic()
> calls with more the more appropriate kmap_local_page() and
> kunmap_local() calls.
> 
> Signed-off-by: Kristen Carlson Accardi <kristen@...ux.intel.com>

Minor comment below.

> ---
>  arch/x86/kernel/cpu/sgx/encl.c  | 12 ++++++------
>  arch/x86/kernel/cpu/sgx/ioctl.c |  4 ++--
>  arch/x86/kernel/cpu/sgx/main.c  |  8 ++++----
>  3 files changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> index f40d64206ded..63dd92bd3288 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -160,8 +160,8 @@ static int __sgx_encl_eldu(struct sgx_encl_page *encl_page,
>  		return ret;
>  
>  	pginfo.addr = encl_page->desc & PAGE_MASK;
> -	pginfo.contents = (unsigned long)kmap_atomic(b.contents);
> -	pcmd_page = kmap_atomic(b.pcmd);
> +	pginfo.contents = (unsigned long)kmap_local_page(b.contents);
> +	pcmd_page = kmap_local_page(b.pcmd);
>  	pginfo.metadata = (unsigned long)pcmd_page + b.pcmd_offset;
>  
>  	if (secs_page)
> @@ -187,8 +187,8 @@ static int __sgx_encl_eldu(struct sgx_encl_page *encl_page,
>  	 */
>  	pcmd_page_empty = !memchr_inv(pcmd_page, 0, PAGE_SIZE);
>  
> -	kunmap_atomic(pcmd_page);
> -	kunmap_atomic((void *)(unsigned long)pginfo.contents);
> +	kunmap_local(pcmd_page);
> +	kunmap_local((void *)(unsigned long)pginfo.contents);
>  
>  	get_page(b.pcmd);
>  	sgx_encl_put_backing(&b);
> @@ -197,10 +197,10 @@ static int __sgx_encl_eldu(struct sgx_encl_page *encl_page,
>  
>  	if (pcmd_page_empty && !reclaimer_writing_to_pcmd(encl, pcmd_first_page)) {
>  		sgx_encl_truncate_backing_page(encl, PFN_DOWN(page_pcmd_off));
> -		pcmd_page = kmap_atomic(b.pcmd);
> +		pcmd_page = kmap_local_page(b.pcmd);
>  		if (memchr_inv(pcmd_page, 0, PAGE_SIZE))
>  			pr_warn("PCMD page not empty after truncate.\n");
> -		kunmap_atomic(pcmd_page);
> +		kunmap_local(pcmd_page);
>  	}
>  
>  	put_page(b.pcmd);
> diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> index ebe79d60619f..f2f918b8b9b1 100644
> --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> @@ -221,11 +221,11 @@ static int __sgx_encl_add_page(struct sgx_encl *encl,
>  	pginfo.secs = (unsigned long)sgx_get_epc_virt_addr(encl->secs.epc_page);
>  	pginfo.addr = encl_page->desc & PAGE_MASK;
>  	pginfo.metadata = (unsigned long)secinfo;
> -	pginfo.contents = (unsigned long)kmap_atomic(src_page);
> +	pginfo.contents = (unsigned long)kmap_local_page(src_page);
>  
>  	ret = __eadd(&pginfo, sgx_get_epc_virt_addr(epc_page));
>  
> -	kunmap_atomic((void *)pginfo.contents);
> +	kunmap_local((void *)pginfo.contents);
>  	put_page(src_page);
>  
>  	return ret ? -EIO : 0;
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index 515e2a5f25bb..4efda5e8cadf 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -159,17 +159,17 @@ static int __sgx_encl_ewb(struct sgx_epc_page *epc_page, void *va_slot,
>  	pginfo.addr = 0;
>  	pginfo.secs = 0;
>  
> -	pginfo.contents = (unsigned long)kmap_atomic(backing->contents);
> -	pginfo.metadata = (unsigned long)kmap_atomic(backing->pcmd) +
> +	pginfo.contents = (unsigned long)kmap_local_page(backing->contents);
> +	pginfo.metadata = (unsigned long)kmap_local_page(backing->pcmd) +
>  			  backing->pcmd_offset;
>  
>  	ret = __ewb(&pginfo, sgx_get_epc_virt_addr(epc_page), va_slot);
>  	set_page_dirty(backing->pcmd);
>  	set_page_dirty(backing->contents);
>  
> -	kunmap_atomic((void *)(unsigned long)(pginfo.metadata -
> +	kunmap_local((void *)(unsigned long)(pginfo.metadata -
>  					      backing->pcmd_offset));

For kunmap_local() one can use any address in the page.  So this can be:

	kunmap_local((void *)(unsigned long)(pginfo.metadata));


Regardless:

Reviewed-by: Ira Weiny <ira.weiny@...el.com>

> -	kunmap_atomic((void *)(unsigned long)pginfo.contents);
> +	kunmap_local((void *)(unsigned long)pginfo.contents);
>  
>  	return ret;
>  }
> -- 
> 2.37.3
>