[MODERATED] Re: ***UNCHECKED*** [patch 3/8] [PATCH v1.3.1 3/7] Linux Patch 3

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, Apr 18, 2018 at 05:37:13PM +0200, speck for Borislav Petkov wrote:
> On Thu, Apr 12, 2018 at 10:26:52PM -0400, speck for konrad.wilk_at_oracle.com wrote:
> > diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> > index 561cb228605a..73f76d0f5181 100644
> > --- a/arch/x86/kernel/cpu/bugs.c
> > +++ b/arch/x86/kernel/cpu/bugs.c
> > @@ -72,6 +72,9 @@ void __init check_bugs(void)
> >  	 */
> >  	if (!direct_gbpages)
> >  		set_memory_4k((unsigned long)__va(0), 1);
> > +
> > +	if (mdd_at_boot())
> > +		wrmsrl(MSR_IA32_SPEC_CTRL, SPEC_CTRL_MDD);
> 
> You can't do this on the common path as that would explode on !Intel.
> 
> Instead, move that check to init_intel().

That won't work. The reason is that check_bugs first calls
identify_boot_cpu() which calls identify_cpu() which calls
this_cpu->init. Once identify_boot_cpu() is done _then_ it walks
through the spectre_v2_select_mitigation() and ssb_select_mitigation().

> 
> And add to init_amd_zn() code reading MSR 0xc0011020, setting bit 10 to
> 1b and then writing it back in the mdd_at_boot() case. We have a define
> for that MSR already - MSR_AMD64_LS_CFG.

I am thinking that perhaps we can add a new function:

From 258854941d792de5de4ffdefcce8f52e8984e2e5 Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Date: Thu, 19 Apr 2018 16:47:38 -0400
Subject: [PATCH] x86/cpu: Add fix_this_cpu to be called _after_ check_bugs and
 at BSP.

We do a lot of things in the check_bugs() - one of the first
things we do is identify_boot_cpu() which calls identify_cpu()
which calls this_cpu->init.

Once identify_boot_cpu() is done _then_ it walks through the
spectre_v2_select_mitigation() and alternative_assembler().

If there are some CPU fix ups _after_ spectre_v2 is done
we can't activate those on the BSP as we have already
called 'this_cpu->init'. Hence add a new function to
fixup CPUs.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 arch/x86/include/asm/processor.h | 1 +
 arch/x86/kernel/cpu/bugs.c       | 1 +
 arch/x86/kernel/cpu/common.c     | 8 ++++++++
 arch/x86/kernel/cpu/cpu.h        | 1 +
 4 files changed, 11 insertions(+)

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index b0ccd4847a58..b22bc9be2385 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -195,6 +195,7 @@ extern void init_amd_cacheinfo(struct cpuinfo_x86 *c);
 
 extern void detect_extended_topology(struct cpuinfo_x86 *c);
 extern void detect_ht(struct cpuinfo_x86 *c);
+extern void apply_cpu_fixes(void);
 
 #ifdef CONFIG_X86_32
 extern int have_cpuid_p(void);
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 4632c26e13e0..9c2987b4f7fa 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -77,6 +77,7 @@ void __init check_bugs(void)
 	if (!direct_gbpages)
 		set_memory_4k((unsigned long)__va(0), 1);
 #endif
+	apply_cpu_fixes();
 }
 
 /* The kernel command line selection */
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index f7d80658cced..a59f7902a7fa 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -955,6 +955,12 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
 	setup_force_cpu_bug(X86_BUG_CPU_SSB);
 };
 
+void apply_cpu_fixes(void)
+{
+	if (this_cpu->c_bug_fix)
+		this_cpu->c_bug_fix(&boot_cpu_data);
+}
+
 /*
  * Do minimum CPU detection early.
  * Fields really needed: vendor, cpuid_level, family, model, mask,
@@ -1311,6 +1317,8 @@ static void identify_cpu(struct cpuinfo_x86 *c)
 #ifdef CONFIG_NUMA
 	numa_add_cpu(smp_processor_id());
 #endif
+	if (this_cpu->c_bug_fix)
+		this_cpu->c_bug_fix(c);
 }
 
 /*
diff --git a/arch/x86/kernel/cpu/cpu.h b/arch/x86/kernel/cpu/cpu.h
index e806b11a99af..7081634caac5 100644
--- a/arch/x86/kernel/cpu/cpu.h
+++ b/arch/x86/kernel/cpu/cpu.h
@@ -15,6 +15,7 @@ struct cpu_dev {
 	void		(*c_identify)(struct cpuinfo_x86 *);
 	void		(*c_detect_tlb)(struct cpuinfo_x86 *);
 	void		(*c_bsp_resume)(struct cpuinfo_x86 *);
+	void		(*c_bug_fix)(struct cpuinfo_x86 *);
 	int		c_x86_vendor;
 #ifdef CONFIG_X86_32
 	/* Optional vendor specific routine to obtain the cache size. */
-- 
2.14.3