From ba696429d290690db967e5f49463df4b2c1314a4 Mon Sep 17 00:00:00 2001
From: Vitaly Kuznetsov <vkuznets@redhat.com>
Date: Wed, 3 Apr 2019 19:03:09 +0200
Subject: [PATCH] x86/hyper-v: Implement EOI assist
Hyper-V TLFS suggests an optimization to avoid imminent VMExit on EOI:
"The OS performs an EOI by atomically writing zero to the EOI Assist field
of the virtual VP assist page and checking whether the "No EOI required"
field was previously zero. If it was, the OS must write to the
HV_X64_APIC_EOI MSR thereby triggering an intercept into the hypervisor."
Implement the optimization in Linux.
Tested-by: Long Li <longli@microsoft.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: K. Y. Srinivasan <kys@microsoft.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michael Kelley (EOSG) <Michael.H.Kelley@microsoft.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Simon Xiao <sixiao@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-hyperv@vger.kernel.org
Link: http://lkml.kernel.org/r/20190403170309.4107-1-vkuznets@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/hyperv/hv_apic.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/arch/x86/hyperv/hv_apic.c b/arch/x86/hyperv/hv_apic.c
index 8eb6fbee8e135..5c056b8aebefc 100644
--- a/arch/x86/hyperv/hv_apic.c
+++ b/arch/x86/hyperv/hv_apic.c
@@ -86,6 +86,11 @@ static void hv_apic_write(u32 reg, u32 val)
static void hv_apic_eoi_write(u32 reg, u32 val)
{
+ struct hv_vp_assist_page *hvp = hv_vp_assist_page[smp_processor_id()];
+
+ if (hvp && (xchg(&hvp->apic_assist, 0) & 0x1))
+ return;
+
wrmsr(HV_X64_MSR_EOI, val, 0);
}
--
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