From ba696429d290690db967e5f49463df4b2c1314a4 Mon Sep 17 00:00:00 2001 From: Vitaly Kuznetsov Date: Wed, 3 Apr 2019 19:03:09 +0200 Subject: 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 Signed-off-by: Vitaly Kuznetsov Cc: Borislav Petkov Cc: Haiyang Zhang Cc: K. Y. Srinivasan Cc: Linus Torvalds Cc: Michael Kelley (EOSG) Cc: Peter Zijlstra Cc: Sasha Levin Cc: Simon Xiao Cc: Stephen Hemminger Cc: Thomas Gleixner Cc: linux-hyperv@vger.kernel.org Link: http://lkml.kernel.org/r/20190403170309.4107-1-vkuznets@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/hyperv/hv_apic.c | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'arch/x86/hyperv') diff --git a/arch/x86/hyperv/hv_apic.c b/arch/x86/hyperv/hv_apic.c index 8eb6fbee8e13..5c056b8aebef 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); } -- cgit v1.2.3