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

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Date:   Thu, 21 Feb 2019 20:56:06 +0000
From:   Joao Martins <joao.m.martins@...cle.com>
To:     Sean Christopherson <sean.j.christopherson@...el.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 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@...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?

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.

> 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