linux-kernel - Re: [PATCH RFC 02/39] KVM: x86/xen: intercept xen hypercalls if enabled

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Message-ID: <20190221182910.GC7224@linux.intel.com>
Date:   Thu, 21 Feb 2019 10:29:10 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Joao Martins <joao.m.martins@...cle.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Ankur Arora <ankur.a.arora@...cle.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org
Subject: Re: [PATCH RFC 02/39] KVM: x86/xen: intercept xen hypercalls if
 enabled

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@...cle.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?
2k+ lines of code is a non-trival amount of baggage for folks that don't
care about running Xen guests.  I've only glanced through the series, so
I've no idea if the resulting code would be an abomination.

>  
>  kvm-intel-y		+= vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o vmx/evmcs.o vmx/nested.o
>  kvm-amd-y		+= svm.o pmu_amd.o