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    SubjectRe: [PATCH RFC 02/39] KVM: x86/xen: intercept xen hypercalls if enabled
    On Thu, Feb 21, 2019 at 08:56:06PM +0000, Joao Martins wrote:
    > On 2/21/19 6:29 PM, Sean Christopherson wrote:
    > > On Wed, Feb 20, 2019 at 08:15:32PM +0000, Joao Martins wrote:
    > >> Add a new exit reason for emulator to handle Xen hypercalls.
    > >> Albeit these are injected only if guest has initialized the Xen
    > >> hypercall page - the hypercall is just a convenience but one
    > >> that is done by pretty much all guests. Hence if the guest
    > >> sets the hypercall page, we assume a Xen guest is going to
    > >> be set up.
    > >>
    > >> Emulator will then panic with:
    > >>
    > >> KVM: unknown exit reason 28
    > >> RAX=0000000000000011 RBX=ffffffff81e03e94 RCX=0000000040000000
    > >> RDX=0000000000000000
    > >> RSI=ffffffff81e03e70 RDI=0000000000000006 RBP=ffffffff81e03e90
    > >> RSP=ffffffff81e03e68
    > >> R8 =73726576206e6558 R9 =ffffffff81e03e90 R10=ffffffff81e03e94
    > >> R11=2e362e34206e6f69
    > >> R12=0000000040000004 R13=ffffffff81e03e8c R14=ffffffff81e03e88
    > >> R15=0000000000000000
    > >> RIP=ffffffff81001228 RFL=00000082 [--S----] CPL=0 II=0 A20=1 SMM=0 HLT=0
    > >> ES =0000 0000000000000000 ffffffff 00c00000
    > >> CS =0010 0000000000000000 ffffffff 00a09b00 DPL=0 CS64 [-RA]
    > >> SS =0000 0000000000000000 ffffffff 00c00000
    > >> DS =0000 0000000000000000 ffffffff 00c00000
    > >> FS =0000 0000000000000000 ffffffff 00c00000
    > >> GS =0000 ffffffff81f34000 ffffffff 00c00000
    > >> LDT=0000 0000000000000000 ffffffff 00c00000
    > >> TR =0020 0000000000000000 00000fff 00808b00 DPL=0 TSS64-busy
    > >> GDT= ffffffff81f3c000 0000007f
    > >> IDT= ffffffff83265000 00000fff
    > >> CR0=80050033 CR2=ffff880001fa6ff8 CR3=0000000001fa6000 CR4=000406a0
    > >> DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000
    > >> DR3=0000000000000000
    > >> DR6=00000000ffff0ff0 DR7=0000000000000400
    > >> EFER=0000000000000d01
    > >> Code=cc cc cc cc cc cc cc cc cc cc cc cc b8 11 00 00 00 0f 01 c1 <c3> cc
    > >> cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc b8 12
    > >> 00 00 00 0f
    > >>
    > >> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
    > >> ---
    > >> arch/x86/include/asm/kvm_host.h | 13 +++++++
    > >> arch/x86/kvm/Makefile | 2 +-
    > >> arch/x86/kvm/trace.h | 33 +++++++++++++++++
    > >> arch/x86/kvm/x86.c | 12 +++++++
    > >> arch/x86/kvm/xen.c | 79 +++++++++++++++++++++++++++++++++++++++++
    > >> arch/x86/kvm/xen.h | 10 ++++++
    > >> include/uapi/linux/kvm.h | 17 ++++++++-
    > >> 7 files changed, 164 insertions(+), 2 deletions(-)
    > >> create mode 100644 arch/x86/kvm/xen.c
    > >> create mode 100644 arch/x86/kvm/xen.h
    > >
    > > ...
    > >
    > >> diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
    > >> index 31ecf7a76d5a..2b46c93c9380 100644
    > >> --- a/arch/x86/kvm/Makefile
    > >> +++ b/arch/x86/kvm/Makefile
    > >> @@ -10,7 +10,7 @@ kvm-$(CONFIG_KVM_ASYNC_PF) += $(KVM)/async_pf.o
    > >>
    > >> kvm-y += x86.o mmu.o emulate.o i8259.o irq.o lapic.o \
    > >> i8254.o ioapic.o irq_comm.o cpuid.o pmu.o mtrr.o \
    > >> - hyperv.o page_track.o debugfs.o
    > >> + hyperv.o xen.o page_track.o debugfs.o
    > >
    > > Can this be wrapped in a config? Or even better, as a loadable module?
    >
    > Turning that into a loadable module might be a little trickier, but I think it
    > is doable if that's what folks/maintainers would prefer.
    >
    > The Xen addition follows the same structure as Hyper-V in kvm (what you suggest
    > here is probably applicable for both). i.e. there's some Xen specific routines
    > for vm/vcpu init/teardown, and timer handling. We would have to place some of
    > those functions into a struct that gets registered at modinit.

    Huh. I never really hooked at the Hyper-V code, for some reason I always
    assumed it was only related to running KVM on Hyper-V. I agree that this
    extra hurdle only makes sense if it's also applied to Hyper-V.

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