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

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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>
This commit is contained in:
Vitaly Kuznetsov
2017-10-06 17:48:54 +02:00
committed by Ingo Molnar
parent d4a2d031dd
commit a3b7424392
3 changed files with 18 additions and 5 deletions
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17
arch/x86/hyperv/mmu.c
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@@ -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)