x86/hyperv: Clear vCPU banks between calls to avoid flushing unneeded vCPUs

hv_flush_pcpu_ex structures are not cleared between calls for performance
reasons (they're variable size up to PAGE_SIZE each) but we must clear
hv_vp_set.bank_contents part of it to avoid flushing unneeded vCPUs. The
rest of the structure is formed correctly.

To do the clearing in an efficient way stash the maximum possible vCPU
number (this may differ from Linux CPU id).

Reported-by: Jork Loeser <Jork.Loeser@microsoft.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Dexuan Cui <decui@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: devel@linuxdriverproject.org
Link: http://lkml.kernel.org/r/20171006154854.18092-1-vkuznets@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 1a8eb550c40f13d8f4f4f5d049e09d323a2bb185..a5db63f728a2f985bde0f1b98f87be4537913cdc 100644 (file)
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -85,6 +85,8 @@ EXPORT_SYMBOL_GPL(hyperv_cs);
 u32 *hv_vp_index;
 EXPORT_SYMBOL_GPL(hv_vp_index);
 
+u32 hv_max_vp_index;
+
 static int hv_cpu_init(unsigned int cpu)
 {
        u64 msr_vp_index;
@@ -93,6 +95,9 @@ static int hv_cpu_init(unsigned int cpu)
 
        hv_vp_index[smp_processor_id()] = msr_vp_index;
 
+       if (msr_vp_index > hv_max_vp_index)
+               hv_max_vp_index = msr_vp_index;
+
        return 0;
 }
 

diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c
index 39e7f6e50919117087fe663e013cd77d12b16b7b..9502d04c0c952eda11dbb6d9f330d5202fb83587 100644 (file)
--- a/arch/x86/hyperv/mmu.c
+++ b/arch/x86/hyperv/mmu.c
@@ -76,6 +76,18 @@ static inline int cpumask_to_vp_set(struct hv_flush_pcpu_ex *flush,
 {
        int cpu, vcpu, vcpu_bank, vcpu_offset, nr_bank = 1;
 
+       /* valid_bank_mask can represent up to 64 banks */
+       if (hv_max_vp_index / 64 >= 64)
+               return 0;
+
+       /*
+        * Clear all banks up to the maximum possible bank as hv_flush_pcpu_ex
+        * structs are not cleared between calls, we risk flushing unneeded
+        * vCPUs otherwise.
+        */
+       for (vcpu_bank = 0; vcpu_bank <= hv_max_vp_index / 64; vcpu_bank++)
+               flush->hv_vp_set.bank_contents[vcpu_bank] = 0;
+
        /*
         * Some banks may end up being empty but this is acceptable.
         */
@@ -83,11 +95,6 @@ static inline int cpumask_to_vp_set(struct hv_flush_pcpu_ex *flush,
                vcpu = hv_cpu_number_to_vp_number(cpu);
                vcpu_bank = vcpu / 64;
                vcpu_offset = vcpu % 64;
-
-               /* valid_bank_mask can represent up to 64 banks */
-               if (vcpu_bank >= 64)
-                       return 0;
-
                __set_bit(vcpu_offset, (unsigned long *)
                          &flush->hv_vp_set.bank_contents[vcpu_bank]);
                if (vcpu_bank >= nr_bank)

diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 738503e1f80c14f1b5720275dd57161509927ef8..530f448fddafff3297f0e97d697309f1a2cf15bf 100644 (file)
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -289,6 +289,7 @@ static inline u64 hv_do_rep_hypercall(u16 code, u16 rep_count, u16 varhead_size,
  * to this information.
  */
 extern u32 *hv_vp_index;
+extern u32 hv_max_vp_index;
 
 /**
  * hv_cpu_number_to_vp_number() - Map CPU to VP.