Commit 02f037d6 authored by Toshi Kani's avatar Toshi Kani Committed by Ingo Molnar
Browse files

x86/mm/pat: Add support of non-default PAT MSR setting 



In preparation for fixing a regression caused by:

  9cd25aac ("x86/mm/pat: Emulate PAT when it is disabled")'

... PAT needs to support a case that PAT MSR is initialized with a
non-default value.

When pat_init() is called and PAT is disabled, it initializes the
PAT table with the BIOS default value. Xen, however, sets PAT MSR
with a non-default value to enable WC. This causes inconsistency
between the PAT table and PAT MSR when PAT is set to disable on Xen.

Change pat_init() to handle the PAT disable cases properly.  Add
init_cache_modes() to handle two cases when PAT is set to disable.

 1. CPU supports PAT: Set PAT table to be consistent with PAT MSR.
 2. CPU does not support PAT: Set PAT table to be consistent with
    PWT and PCD bits in a PTE.

Note, __init_cache_modes(), renamed from pat_init_cache_modes(),
will be changed to a static function in a later patch.

Signed-off-by: default avatarToshi Kani <toshi.kani@hpe.com>
Reviewed-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: elliott@hpe.com
Cc: konrad.wilk@oracle.com
Cc: paul.gortmaker@windriver.com
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1458769323-24491-2-git-send-email-toshi.kani@hpe.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 1993b176

arch/x86/include/asm/pat.h

+1 −1
Original line number Diff line number Diff line
@@ -6,7 +6,7 @@ 


bool pat_enabled(void);

extern void pat_init(void);

void pat_init_cache_modes(u64);

void __init_cache_modes(u64);



extern int reserve_memtype(u64 start, u64 end,

		enum page_cache_mode req_pcm, enum page_cache_mode *ret_pcm);

arch/x86/mm/pat.c

+53 −20
Original line number Diff line number Diff line
@@ -181,7 +181,7 @@ 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(u64 pat)

void __init_cache_modes(u64 pat)

{

	enum page_cache_mode cache;

	char pat_msg[33];
@@ -207,9 +207,6 @@ static void pat_bsp_init(u64 pat) 
		return;

	}



	if (!pat_enabled())

		goto done;



	rdmsrl(MSR_IA32_CR_PAT, tmp_pat);

	if (!tmp_pat) {

		pat_disable("PAT MSR is 0, disabled.");
@@ -218,15 +215,11 @@ static void pat_bsp_init(u64 pat) 


	wrmsrl(MSR_IA32_CR_PAT, pat);



done:

	pat_init_cache_modes(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
@@ -238,18 +231,32 @@ static void pat_ap_init(u64 pat) 
	wrmsrl(MSR_IA32_CR_PAT, pat);

}



void pat_init(void)

static void init_cache_modes(void)

{

	u64 pat;

	struct cpuinfo_x86 *c = &boot_cpu_data;

	u64 pat = 0;

	static int init_cm_done;



	if (!pat_enabled()) {

	if (init_cm_done)

		return;



	if (boot_cpu_has(X86_FEATURE_PAT)) {

		/*

		 * CPU supports PAT. Set PAT table to be consistent with

		 * PAT MSR. This case supports "nopat" boot option, and

		 * virtual machine environments which support PAT without

		 * MTRRs. In specific, Xen has unique setup to PAT MSR.

		 *

		 * If PAT MSR returns 0, it is considered invalid and emulates

		 * as No PAT.

		 */

		rdmsrl(MSR_IA32_CR_PAT, pat);

	}



	if (!pat) {

		/*

		 * 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.

		 * cache bits, PWT (Write Through) and PCD (Cache Disable).

		 * This setup is also the same as the BIOS default setup.

		 *

		 * PTE encoding:

		 *
@@ -266,8 +273,34 @@ void pat_init(void) 
		 */

		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);

	}



	__init_cache_modes(pat);



	init_cm_done = 1;

}



/**

 * pat_init - Initialize PAT MSR and PAT table

 *

 * This function initializes PAT MSR and PAT table with an OS-defined value

 * to enable additional cache attributes, WC and WT.

 *

 * This function must be called on all CPUs using the specific sequence of

 * operations defined in Intel SDM. mtrr_rendezvous_handler() provides this

 * procedure for PAT.

 */

void pat_init(void)

{

	u64 pat;

	struct cpuinfo_x86 *c = &boot_cpu_data;



	if (!pat_enabled()) {

		init_cache_modes();

		return;

	}



	} else if ((c->x86_vendor == X86_VENDOR_INTEL) &&

	if ((c->x86_vendor == X86_VENDOR_INTEL) &&

	    (((c->x86 == 0x6) && (c->x86_model <= 0xd)) ||

	     ((c->x86 == 0xf) && (c->x86_model <= 0x6)))) {

		/*

arch/x86/xen/enlighten.c

+1 −1
Original line number Diff line number Diff line
@@ -1623,7 +1623,7 @@ asmlinkage __visible void __init xen_start_kernel(void) 
	 * configuration.

	 */

	rdmsrl(MSR_IA32_CR_PAT, pat);

	pat_init_cache_modes(pat);

	__init_cache_modes(pat);



	/* keep using Xen gdt for now; no urgent need to change it */

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