Re: [PATCH 2/4] x86/pat: Merge pat_init_cache_modes() into its caller

From: Juergen Gross <jgross@suse.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Andy Lutomirski <luto@amacapital.net>,
	arnd@arndb.de, Elliott@hp.com, hch@lst.de, hmh@hmh.eng.br,
	"H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
	konrad.wilk@oracle.com, linux-mm <linux-mm@kvack.org>,
	linux-nvdimm@lists.01.org, "Luis R. Rodriguez" <mcgrof@suse.com>,
	stefan.bader@canonical.com, Thomas Gleixner <tglx@linutronix.de>,
	Toshi Kani <toshi.kani@hp.com>, x86-ml <x86@kernel.org>,
	yigal@plexistor.com, lkml <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/4] x86/pat: Merge pat_init_cache_modes() into its caller
Date: Sun, 31 May 2015 13:02:21 +0200	[thread overview]
Message-ID: <556AEA3D.4000502@suse.com> (raw)
In-Reply-To: <20150531102338.GB20440@pd.tnic>

On 05/31/2015 12:23 PM, Borislav Petkov wrote:
> On Sun, May 31, 2015 at 11:48:04AM +0200, Borislav Petkov wrote:
>> From: Borislav Petkov <bp@suse.de>
>>
>> This way we can pass pat MSR value directly.
>
> This breaks xen as that function is used there, doh. :-\
>
> Jürgen,
>
> can you check the enlighten.c changes below please?

Acked-by: Juergen Gross <jgross@suse.com>

>
> I'm reading xen's PAT config from MSR_IA32_CR_PAT and handing it down to
> pat_init_cache_modes(). That shouldn't change current behavior AFAICT
> because pat_init_cache_modes() did it itself before.
>
> Right?
>
> Thanks.
>
> ---
> Author: Borislav Petkov <bp@suse.de>
> Date:   Sat May 30 13:09:55 2015 +0200
>
>      x86/pat: Emulate PAT when it is disabled
>
>      In the case when PAT is disabled on the command line with "nopat" or
>      when virtualization doesn't support PAT (correctly) - see
>
>        9d34cfdf4796 ("x86: Don't rely on VMWare emulating PAT MSR correctly").
>
>      we emulate it using the PWT and PCD cache attribute bits. Get rid of
>      boot_pat_state while at it.
>
>      Based on a conglomerate patch from Toshi Kani.
>
>      Signed-off-by: Borislav Petkov <bp@suse.de>
>      Cc: Andrew Morton <akpm@linux-foundation.org>
>      Cc: Andy Lutomirski <luto@amacapital.net>
>      Cc: arnd@arndb.de
>      Cc: Elliott@hp.com
>      Cc: hch@lst.de
>      Cc: hmh@hmh.eng.br
>      Cc: H. Peter Anvin <hpa@zytor.com>
>      Cc: Ingo Molnar <mingo@redhat.com>
>      Cc: jgross@suse.com
>      Cc: konrad.wilk@oracle.com
>      Cc: linux-mm <linux-mm@kvack.org>
>      Cc: linux-nvdimm@lists.01.org
>      Cc: Luis R. Rodriguez <mcgrof@suse.com>
>      Cc: stefan.bader@canonical.com
>      Cc: Thomas Gleixner <tglx@linutronix.de>
>      Cc: Toshi Kani <toshi.kani@hp.com>
>      Cc: x86-ml <x86@kernel.org>
>      Cc: yigal@plexistor.com
>
> diff --git a/arch/x86/include/asm/pat.h b/arch/x86/include/asm/pat.h
> index cdcff7f7f694..ca6c228d5e62 100644
> --- a/arch/x86/include/asm/pat.h
> +++ b/arch/x86/include/asm/pat.h
> @@ -6,7 +6,7 @@
>
>   bool pat_enabled(void);
>   extern void pat_init(void);
> -void pat_init_cache_modes(void);
> +void pat_init_cache_modes(u64);
>
>   extern int reserve_memtype(u64 start, u64 end,
>   		enum page_cache_mode req_pcm, enum page_cache_mode *ret_pcm);
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index 1d553186c434..8533b46e6bee 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -40,7 +40,7 @@
>    */
>   uint16_t __cachemode2pte_tbl[_PAGE_CACHE_MODE_NUM] = {
>   	[_PAGE_CACHE_MODE_WB      ]	= 0         | 0        ,
> -	[_PAGE_CACHE_MODE_WC      ]	= _PAGE_PWT | 0        ,
> +	[_PAGE_CACHE_MODE_WC      ]	= 0         | _PAGE_PCD,
>   	[_PAGE_CACHE_MODE_UC_MINUS]	= 0         | _PAGE_PCD,
>   	[_PAGE_CACHE_MODE_UC      ]	= _PAGE_PWT | _PAGE_PCD,
>   	[_PAGE_CACHE_MODE_WT      ]	= 0         | _PAGE_PCD,
> @@ -50,11 +50,11 @@ EXPORT_SYMBOL(__cachemode2pte_tbl);
>
>   uint8_t __pte2cachemode_tbl[8] = {
>   	[__pte2cm_idx( 0        | 0         | 0        )] = _PAGE_CACHE_MODE_WB,
> -	[__pte2cm_idx(_PAGE_PWT | 0         | 0        )] = _PAGE_CACHE_MODE_WC,
> +	[__pte2cm_idx(_PAGE_PWT | 0         | 0        )] = _PAGE_CACHE_MODE_UC_MINUS,
>   	[__pte2cm_idx( 0        | _PAGE_PCD | 0        )] = _PAGE_CACHE_MODE_UC_MINUS,
>   	[__pte2cm_idx(_PAGE_PWT | _PAGE_PCD | 0        )] = _PAGE_CACHE_MODE_UC,
>   	[__pte2cm_idx( 0        | 0         | _PAGE_PAT)] = _PAGE_CACHE_MODE_WB,
> -	[__pte2cm_idx(_PAGE_PWT | 0         | _PAGE_PAT)] = _PAGE_CACHE_MODE_WC,
> +	[__pte2cm_idx(_PAGE_PWT | 0         | _PAGE_PAT)] = _PAGE_CACHE_MODE_UC_MINUS,
>   	[__pte2cm_idx(0         | _PAGE_PCD | _PAGE_PAT)] = _PAGE_CACHE_MODE_UC_MINUS,
>   	[__pte2cm_idx(_PAGE_PWT | _PAGE_PCD | _PAGE_PAT)] = _PAGE_CACHE_MODE_UC,
>   };
> diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
> index 476d0780560f..6dc7826e4797 100644
> --- a/arch/x86/mm/pat.c
> +++ b/arch/x86/mm/pat.c
> @@ -68,8 +68,6 @@ static int __init pat_debug_setup(char *str)
>   }
>   __setup("debugpat", pat_debug_setup);
>
> -static u64 __read_mostly boot_pat_state;
> -
>   #ifdef CONFIG_X86_PAT
>   /*
>    * X86 PAT uses page flags WC and Uncached together to keep track of
> @@ -177,14 +175,12 @@ static enum page_cache_mode pat_get_cache_mode(unsigned pat_val, char *msg)
>    * configuration.
>    * Using lower indices is preferred, so we start with highest index.
>    */
> -void pat_init_cache_modes(void)
> +void pat_init_cache_modes(u64 pat)
>   {
> -	int i;
>   	enum page_cache_mode cache;
>   	char pat_msg[33];
> -	u64 pat;
> +	int i;
>
> -	rdmsrl(MSR_IA32_CR_PAT, pat);
>   	pat_msg[32] = 0;
>   	for (i = 7; i >= 0; i--) {
>   		cache = pat_get_cache_mode((pat >> (i * 8)) & 7,
> @@ -198,24 +194,33 @@ void pat_init_cache_modes(void)
>
>   static void pat_bsp_init(u64 pat)
>   {
> +	u64 tmp_pat;
> +
>   	if (!cpu_has_pat) {
>   		pat_disable("PAT not supported by CPU.");
>   		return;
>   	}
>
> -	rdmsrl(MSR_IA32_CR_PAT, boot_pat_state);
> -	if (!boot_pat_state) {
> +	if (!pat_enabled())
> +		goto done;
> +
> +	rdmsrl(MSR_IA32_CR_PAT, tmp_pat);
> +	if (!tmp_pat) {
>   		pat_disable("PAT MSR is 0, disabled.");
>   		return;
>   	}
>
>   	wrmsrl(MSR_IA32_CR_PAT, pat);
>
> -	pat_init_cache_modes();
> +done:
> +	pat_init_cache_modes(pat);
>   }
>
>   static void pat_ap_init(u64 pat)
>   {
> +	if (!pat_enabled())
> +		return;
> +
>   	if (!cpu_has_pat) {
>   		/*
>   		 * If this happens we are on a secondary CPU, but switched to
> @@ -231,25 +236,45 @@ void pat_init(void)
>   {
>   	u64 pat;
>
> -	if (!pat_enabled())
> -		return;
> -
> -	/*
> -	 * Set PWT to Write-Combining. All other bits stay the same:
> -	 *
> -	 * PTE encoding used in Linux:
> -	 *      PAT
> -	 *      |PCD
> -	 *      ||PWT
> -	 *      |||
> -	 *      000 WB		_PAGE_CACHE_WB
> -	 *      001 WC		_PAGE_CACHE_WC
> -	 *      010 UC-		_PAGE_CACHE_UC_MINUS
> -	 *      011 UC		_PAGE_CACHE_UC
> -	 * PAT bit unused
> -	 */
> -	pat = PAT(0, WB) | PAT(1, WC) | PAT(2, UC_MINUS) | PAT(3, UC) |
> -	      PAT(4, WB) | PAT(5, WC) | PAT(6, UC_MINUS) | PAT(7, UC);
> +	if (!pat_enabled()) {
> +		/*
> +		 * No PAT. Emulate the PAT table that corresponds to the two
> +		 * cache bits, PWT (Write Through) and PCD (Cache Disable). This
> +		 * setup is the same as the BIOS default setup when the system
> +		 * has PAT but the "nopat" boot option has been specified. This
> +		 * emulated PAT table is used when MSR_IA32_CR_PAT returns 0.
> +		 *
> +		 * PTE encoding used:
> +		 *
> +		 *       PCD
> +		 *       |PWT  PAT
> +		 *       ||    slot
> +		 *       00    0    WB : _PAGE_CACHE_MODE_WB
> +		 *       01    1    WT : _PAGE_CACHE_MODE_WT
> +		 *       10    2    UC-: _PAGE_CACHE_MODE_UC_MINUS
> +		 *       11    3    UC : _PAGE_CACHE_MODE_UC
> +		 *
> +		 * NOTE: When WC or WP is used, it is redirected to UC- per
> +		 * the default setup in __cachemode2pte_tbl[].
> +		 */
> +		pat = PAT(0, WB) | PAT(1, WT) | PAT(2, UC_MINUS) | PAT(3, UC) |
> +		      PAT(4, WB) | PAT(5, WT) | PAT(6, UC_MINUS) | PAT(7, UC);
> +	} else {
> +		/*
> +		 * PTE encoding used in Linux:
> +		 *      PAT
> +		 *      |PCD
> +		 *      ||PWT
> +		 *      |||
> +		 *      000 WB          _PAGE_CACHE_WB
> +		 *      001 WC          _PAGE_CACHE_WC
> +		 *      010 UC-         _PAGE_CACHE_UC_MINUS
> +		 *      011 UC          _PAGE_CACHE_UC
> +		 * PAT bit unused
> +		 */
> +		pat = PAT(0, WB) | PAT(1, WC) | PAT(2, UC_MINUS) | PAT(3, UC) |
> +		      PAT(4, WB) | PAT(5, WC) | PAT(6, UC_MINUS) | PAT(7, UC);
> +	}
>
>   	if (!boot_cpu_done) {
>   		pat_bsp_init(pat);
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index 46957ead3060..53233a9beea9 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -1467,6 +1467,7 @@ asmlinkage __visible void __init xen_start_kernel(void)
>   {
>   	struct physdev_set_iopl set_iopl;
>   	unsigned long initrd_start = 0;
> +	u64 pat;
>   	int rc;
>
>   	if (!xen_start_info)
> @@ -1574,8 +1575,8 @@ asmlinkage __visible void __init xen_start_kernel(void)
>   	 * Modify the cache mode translation tables to match Xen's PAT
>   	 * configuration.
>   	 */
> -
> -	pat_init_cache_modes();
> +	rdmsrl(MSR_IA32_CR_PAT, pat);
> +	pat_init_cache_modes(pat);
>
>   	/* keep using Xen gdt for now; no urgent need to change it */
>
>
>

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>