[v10,16/16] microcode/intel: writeback and invalidate cache conditionally

Commit Message

Chao Gao Sept. 12, 2019, 7:22 a.m. UTC

It is needed to mitigate some issues on this specific Broadwell CPU.

Signed-off-by: Chao Gao <[e-mail]>
---
 xen/arch/x86/microcode_intel.c | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)

Comments

Jan Beulich Sept. 13, 2019, 9:32 a.m. UTC | #1

On 12.09.2019 09:22, Chao Gao wrote:
> --- a/xen/arch/x86/microcode_intel.c
> +++ b/xen/arch/x86/microcode_intel.c
> @@ -305,6 +305,31 @@ static bool is_blacklisted(void)
>      return false;
>  }
>  
> +static void microcode_quirk(void)
> +{
> +    struct cpuinfo_x86 *c;

const

> +    uint64_t llc_size;
> +
> +    /*
> +     * Don't refer to current_cpu_data, which isn't fully initialized
> +     * before this stage.
> +     */
> +    if ( system_state < SYS_STATE_smp_boot )
> +        return;

If the workaround is needed, why would it not be needed for the BSP?

> +    c = &current_cpu_data;
> +    llc_size = c->x86_cache_size * 1024ULL;
> +    do_div(llc_size, c->x86_max_cores);

Instead of the local variable, ...

> +
> +    /*
> +     * To mitigate some issues on this specific Broadwell CPU, writeback and
> +     * invalidate cache regardless of ucode revision.
> +     */
> +    if ( c->x86 == 6 && c->x86_model == 0x4F && c->x86_mask == 0x1 &&
> +         llc_size > 2621440 )

... why don't you compare c->x86_cache_size / c->x86_max_cores
against 2560 here? Is there any risk of truncating relevant low
bits?

Jan

Patch

diff --git a/xen/arch/x86/microcode_intel.c b/xen/arch/x86/microcode_intel.c
index bcef668..4e5e7f9 100644
--- a/xen/arch/x86/microcode_intel.c
+++ b/xen/arch/x86/microcode_intel.c
@@ -305,6 +305,31 @@  static bool is_blacklisted(void)
     return false;
 }
 
+static void microcode_quirk(void)
+{
+    struct cpuinfo_x86 *c;
+    uint64_t llc_size;
+
+    /*
+     * Don't refer to current_cpu_data, which isn't fully initialized
+     * before this stage.
+     */
+    if ( system_state < SYS_STATE_smp_boot )
+        return;
+
+    c = &current_cpu_data;
+    llc_size = c->x86_cache_size * 1024ULL;
+    do_div(llc_size, c->x86_max_cores);
+
+    /*
+     * To mitigate some issues on this specific Broadwell CPU, writeback and
+     * invalidate cache regardless of ucode revision.
+     */
+    if ( c->x86 == 6 && c->x86_model == 0x4F && c->x86_mask == 0x1 &&
+         llc_size > 2621440 )
+        wbinvd();
+}
+
 static int apply_microcode(const struct microcode_patch *patch)
 {
     uint64_t msr_content;
@@ -323,6 +348,8 @@  static int apply_microcode(const struct microcode_patch *patch)
 
     BUG_ON(local_irq_is_enabled());
 
+    microcode_quirk();
+
     /* write microcode via MSR 0x79 */
     wrmsrl(MSR_IA32_UCODE_WRITE, (unsigned long)mc_intel->bits);
     wrmsrl(MSR_IA32_UCODE_REV, 0x0ULL);