From 3ff42da5048649503e343a32be37b14a6a4e8aaf Mon Sep 17 00:00:00 2001 From: Andreas Herrmann Date: Thu, 12 Mar 2009 17:39:37 +0100 Subject: x86: mtrr: don't modify RdDram/WrDram bits of fixed MTRRs Impact: bug fix + BIOS workaround BIOS is expected to clear the SYSCFG[MtrrFixDramModEn] on AMD CPUs after fixed MTRRs are configured. Some BIOSes do not clear SYSCFG[MtrrFixDramModEn] on BP (and on APs). This can lead to obfuscation in Linux when this bit is not cleared on BP but cleared on APs. A consequence of this is that the saved fixed-MTRR state (from BP) differs from the fixed-MTRRs of APs -- because RdDram/WrDram bits are read as zero when SYSCFG[MtrrFixDramModEn] is cleared -- and Linux tries to sync fixed-MTRR state from BP to AP. This implies that Linux sets SYSCFG[MtrrFixDramEn] and activates those bits. More important is that (some) systems change these bits in SMM when ACPI is enabled. Hence it is racy if Linux modifies RdMem/WrMem bits, too. (1) The patch modifies an old fix from Bernhard Kaindl to get suspend/resume working on some Acer Laptops. Bernhard's patch tried to sync RdMem/WrMem bits of fixed MTRR registers and that helped on those old Laptops. (Don't ask me why -- can't test it myself). But this old problem was not the motivation for the patch. (See http://lkml.org/lkml/2007/4/3/110) (2) The more important effect is to fix issues on some more current systems. On those systems Linux panics or just freezes, see http://bugzilla.kernel.org/show_bug.cgi?id=11541 (and also duplicates of this bug: http://bugzilla.kernel.org/show_bug.cgi?id=11737 http://bugzilla.kernel.org/show_bug.cgi?id=11714) The affected systems boot only using acpi=ht, acpi=off or when the kernel is built with CONFIG_MTRR=n. The acpi options prevent full enablement of ACPI. Obviously when ACPI is enabled the BIOS/SMM modfies RdMem/WrMem bits. When CONFIG_MTRR=y Linux also accesses and modifies those bits when it needs to sync fixed-MTRRs across cores (Bernhard's fix, see (1)). How do you synchronize that? You can't. As a consequence Linux shouldn't touch those bits at all (Rationale are AMD's BKDGs which recommend to clear the bit that makes RdMem/WrMem accessible). This is the purpose of this patch. And (so far) this suffices to fix (1) and (2). I suggest not to touch RdDram/WrDram bits of fixed-MTRRs and SYSCFG[MtrrFixDramEn] and to clear SYSCFG[MtrrFixDramModEn] as suggested by AMD K8, and AMD family 10h/11h BKDGs. BIOS is expected to do this anyway. This should avoid that Linux and SMM tread on each other's toes ... Signed-off-by: Andreas Herrmann Cc: trenn@suse.de Cc: Yinghai Lu LKML-Reference: <20090312163937.GH20716@alberich.amd.com> Cc: Signed-off-by: Ingo Molnar --- arch/x86/kernel/cpu/mtrr/generic.c | 51 ++++++++++++++++++++++---------------- 1 file changed, 30 insertions(+), 21 deletions(-) (limited to 'arch/x86/kernel/cpu/mtrr') diff --git a/arch/x86/kernel/cpu/mtrr/generic.c b/arch/x86/kernel/cpu/mtrr/generic.c index 964403520100..950c434f793d 100644 --- a/arch/x86/kernel/cpu/mtrr/generic.c +++ b/arch/x86/kernel/cpu/mtrr/generic.c @@ -33,6 +33,32 @@ u64 mtrr_tom2; struct mtrr_state_type mtrr_state = {}; EXPORT_SYMBOL_GPL(mtrr_state); +/** + * BIOS is expected to clear MtrrFixDramModEn bit, see for example + * "BIOS and Kernel Developer's Guide for the AMD Athlon 64 and AMD + * Opteron Processors" (26094 Rev. 3.30 February 2006), section + * "13.2.1.2 SYSCFG Register": "The MtrrFixDramModEn bit should be set + * to 1 during BIOS initalization of the fixed MTRRs, then cleared to + * 0 for operation." + */ +static inline void k8_check_syscfg_dram_mod_en(void) +{ + u32 lo, hi; + + if (!((boot_cpu_data.x86_vendor == X86_VENDOR_AMD) && + (boot_cpu_data.x86 >= 0x0f))) + return; + + rdmsr(MSR_K8_SYSCFG, lo, hi); + if (lo & K8_MTRRFIXRANGE_DRAM_MODIFY) { + printk(KERN_ERR FW_WARN "MTRR: CPU %u: SYSCFG[MtrrFixDramModEn]" + " not cleared by BIOS, clearing this bit\n", + smp_processor_id()); + lo &= ~K8_MTRRFIXRANGE_DRAM_MODIFY; + mtrr_wrmsr(MSR_K8_SYSCFG, lo, hi); + } +} + /* * Returns the effective MTRR type for the region * Error returns: @@ -166,6 +192,8 @@ get_fixed_ranges(mtrr_type * frs) unsigned int *p = (unsigned int *) frs; int i; + k8_check_syscfg_dram_mod_en(); + rdmsr(MTRRfix64K_00000_MSR, p[0], p[1]); for (i = 0; i < 2; i++) @@ -305,28 +333,11 @@ void mtrr_wrmsr(unsigned msr, unsigned a, unsigned b) smp_processor_id(), msr, a, b); } -/** - * Enable and allow read/write of extended fixed-range MTRR bits on K8 CPUs - * see AMD publication no. 24593, chapter 3.2.1 for more information - */ -static inline void k8_enable_fixed_iorrs(void) -{ - unsigned lo, hi; - - rdmsr(MSR_K8_SYSCFG, lo, hi); - mtrr_wrmsr(MSR_K8_SYSCFG, lo - | K8_MTRRFIXRANGE_DRAM_ENABLE - | K8_MTRRFIXRANGE_DRAM_MODIFY, hi); -} - /** * set_fixed_range - checks & updates a fixed-range MTRR if it differs from the value it should have * @msr: MSR address of the MTTR which should be checked and updated * @changed: pointer which indicates whether the MTRR needed to be changed * @msrwords: pointer to the MSR values which the MSR should have - * - * If K8 extentions are wanted, update the K8 SYSCFG MSR also. - * See AMD publication no. 24593, chapter 7.8.1, page 233 for more information. */ static void set_fixed_range(int msr, bool *changed, unsigned int *msrwords) { @@ -335,10 +346,6 @@ static void set_fixed_range(int msr, bool *changed, unsigned int *msrwords) rdmsr(msr, lo, hi); if (lo != msrwords[0] || hi != msrwords[1]) { - if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD && - (boot_cpu_data.x86 >= 0x0f && boot_cpu_data.x86 <= 0x11) && - ((msrwords[0] | msrwords[1]) & K8_MTRR_RDMEM_WRMEM_MASK)) - k8_enable_fixed_iorrs(); mtrr_wrmsr(msr, msrwords[0], msrwords[1]); *changed = true; } @@ -426,6 +433,8 @@ static int set_fixed_ranges(mtrr_type * frs) bool changed = false; int block=-1, range; + k8_check_syscfg_dram_mod_en(); + while (fixed_range_blocks[++block].ranges) for (range=0; range < fixed_range_blocks[block].ranges; range++) set_fixed_range(fixed_range_blocks[block].base_msr + range, -- cgit v1.2.3