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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 2/2] x86/vm_event: Allow returning i-cache for emulation
On 09/15/16 20:08, Razvan Cojocaru wrote:
> On 09/15/16 19:36, Tamas K Lengyel wrote:
>> On Wed, Sep 14, 2016 at 1:58 AM, Razvan Cojocaru
>> <rcojocaru@xxxxxxxxxxxxxxx> wrote:
>>> On 09/13/2016 09:12 PM, Tamas K Lengyel wrote:
>>>> When emulating instructions the emulator maintains a small i-cache fetched
>>>> from the guest memory. This patch extends the vm_event interface to allow
>>>> returning this i-cache via the vm_event response instead.
>>>>
>>>> When responding to a SOFTWARE_BREAKPOINT event (INT3) the monitor
>>>> subscriber
>>>> normally has to remove the INT3 from memory - singlestep - place back INT3
>>>> to allow the guest to continue execution. This routine however is
>>>> susceptible
>>>> to a race-condition on multi-vCPU guests. By allowing the subscriber to
>>>> return
>>>> the i-cache to be used for emulation it can side-step the problem by
>>>> returning
>>>> a clean buffer without the INT3 present.
>>>>
>>>> As part of this patch we rename hvm_mem_access_emulate_one to
>>>> hvm_emulate_one_vm_event to better reflect that it is used in various
>>>> vm_event
>>>> scenarios now, not just in response to mem_access events.
>>>>
>>>> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>
>>>> ---
>>>> Cc: Paul Durrant <paul.durrant@xxxxxxxxxx>
>>>> Cc: Jan Beulich <jbeulich@xxxxxxxx>
>>>> Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>>> Cc: Jun Nakajima <jun.nakajima@xxxxxxxxx>
>>>> Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
>>>> Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
>>>> Cc: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
>>>> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>>>> Cc: Julien Grall <julien.grall@xxxxxxx>
>>>>
>>>> Note: This patch only has been compile-tested.
>>>> ---
>>>> xen/arch/x86/hvm/emulate.c | 44
>>>> ++++++++++++++++++++++++++-------------
>>>> xen/arch/x86/hvm/hvm.c | 9 +++++---
>>>> xen/arch/x86/hvm/vmx/vmx.c | 1 +
>>>> xen/arch/x86/vm_event.c | 9 +++++++-
>>>> xen/common/vm_event.c | 1 -
>>>> xen/include/asm-x86/hvm/emulate.h | 8 ++++---
>>>> xen/include/asm-x86/vm_event.h | 3 ++-
>>>> xen/include/public/vm_event.h | 16 +++++++++++++-
>>>> 8 files changed, 67 insertions(+), 24 deletions(-)
>>>>
>>>> diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
>>>> index cc25676..504ed35 100644
>>>> --- a/xen/arch/x86/hvm/emulate.c
>>>> +++ b/xen/arch/x86/hvm/emulate.c
>>>> @@ -76,9 +76,9 @@ static int set_context_data(void *buffer, unsigned int
>>>> size)
>>>> if ( curr->arch.vm_event )
>>>> {
>>>> unsigned int safe_size =
>>>> - min(size, curr->arch.vm_event->emul_read_data.size);
>>>> + min(size, curr->arch.vm_event->emul_read.size);
>>>>
>>>> - memcpy(buffer, curr->arch.vm_event->emul_read_data.data,
>>>> safe_size);
>>>> + memcpy(buffer, curr->arch.vm_event->emul_read.data, safe_size);
>>>> memset(buffer + safe_size, 0, size - safe_size);
>>>> return X86EMUL_OKAY;
>>>> }
>>>> @@ -827,7 +827,7 @@ static int hvmemul_read(
>>>> struct hvm_emulate_ctxt *hvmemul_ctxt =
>>>> container_of(ctxt, struct hvm_emulate_ctxt, ctxt);
>>>>
>>>> - if ( unlikely(hvmemul_ctxt->set_context) )
>>>> + if ( unlikely(hvmemul_ctxt->set_context_data) )
>>>> return set_context_data(p_data, bytes);
>>>>
>>>> return __hvmemul_read(
>>>> @@ -1029,7 +1029,7 @@ static int hvmemul_cmpxchg(
>>>> struct hvm_emulate_ctxt *hvmemul_ctxt =
>>>> container_of(ctxt, struct hvm_emulate_ctxt, ctxt);
>>>>
>>>> - if ( unlikely(hvmemul_ctxt->set_context) )
>>>> + if ( unlikely(hvmemul_ctxt->set_context_data) )
>>>> {
>>>> int rc = set_context_data(p_new, bytes);
>>>>
>>>> @@ -1122,7 +1122,7 @@ static int hvmemul_rep_outs(
>>>> p2m_type_t p2mt;
>>>> int rc;
>>>>
>>>> - if ( unlikely(hvmemul_ctxt->set_context) )
>>>> + if ( unlikely(hvmemul_ctxt->set_context_data) )
>>>> return hvmemul_rep_outs_set_context(src_seg, src_offset, dst_port,
>>>> bytes_per_rep, reps, ctxt);
>>>>
>>>> @@ -1264,7 +1264,7 @@ static int hvmemul_rep_movs(
>>>> if ( buf == NULL )
>>>> return X86EMUL_UNHANDLEABLE;
>>>>
>>>> - if ( unlikely(hvmemul_ctxt->set_context) )
>>>> + if ( unlikely(hvmemul_ctxt->set_context_data) )
>>>> {
>>>> rc = set_context_data(buf, bytes);
>>>>
>>>> @@ -1470,7 +1470,7 @@ static int hvmemul_read_io(
>>>>
>>>> *val = 0;
>>>>
>>>> - if ( unlikely(hvmemul_ctxt->set_context) )
>>>> + if ( unlikely(hvmemul_ctxt->set_context_data) )
>>>> return set_context_data(val, bytes);
>>>>
>>>> return hvmemul_do_pio_buffer(port, bytes, IOREQ_READ, val);
>>>> @@ -1793,7 +1793,14 @@ static int _hvm_emulate_one(struct hvm_emulate_ctxt
>>>> *hvmemul_ctxt,
>>>> pfec |= PFEC_user_mode;
>>>>
>>>> hvmemul_ctxt->insn_buf_eip = regs->eip;
>>>> - if ( !vio->mmio_insn_bytes )
>>>> +
>>>> + if ( unlikely(hvmemul_ctxt->set_context_insn) && curr->arch.vm_event )
>>>> + {
>>>> + hvmemul_ctxt->insn_buf_bytes =
>>>> sizeof(curr->arch.vm_event->emul_insn);
>>>> + memcpy(hvmemul_ctxt->insn_buf, &curr->arch.vm_event->emul_insn,
>>>> + hvmemul_ctxt->insn_buf_bytes);
>>>> + }
>>>> + else if ( !vio->mmio_insn_bytes )
>>>> {
>>>> hvmemul_ctxt->insn_buf_bytes =
>>>> hvm_get_insn_bytes(curr, hvmemul_ctxt->insn_buf) ?:
>>>> @@ -1931,7 +1938,7 @@ int hvm_emulate_one_mmio(unsigned long mfn, unsigned
>>>> long gla)
>>>> return rc;
>>>> }
>>>>
>>>> -void hvm_mem_access_emulate_one(enum emul_kind kind, unsigned int trapnr,
>>>> +void hvm_emulate_one_vm_event(enum emul_kind kind, unsigned int trapnr,
>>>> unsigned int errcode)
>>>> {
>>>> struct hvm_emulate_ctxt ctx = {{ 0 }};
>>>> @@ -1944,11 +1951,19 @@ void hvm_mem_access_emulate_one(enum emul_kind
>>>> kind, unsigned int trapnr,
>>>> case EMUL_KIND_NOWRITE:
>>>> rc = hvm_emulate_one_no_write(&ctx);
>>>> break;
>>>> - case EMUL_KIND_SET_CONTEXT:
>>>> - ctx.set_context = 1;
>>>> - /* Intentional fall-through. */
>>>> - default:
>>>> + case EMUL_KIND_SET_CONTEXT_DATA:
>>>> + ctx.set_context_data = 1;
>>>> + rc = hvm_emulate_one(&ctx);
>>>> + break;
>>>> + case EMUL_KIND_SET_CONTEXT_INSN:
>>>> + ctx.set_context_insn = 1;
>>>> rc = hvm_emulate_one(&ctx);
>>>> + break;
>>>> + case EMUL_KIND_NORMAL:
>>>> + rc = hvm_emulate_one(&ctx);
>>>> + break;
>>>> + default:
>>>> + return;
>>>> }
>>>>
>>>> switch ( rc )
>>>> @@ -1983,7 +1998,8 @@ void hvm_emulate_prepare(
>>>> hvmemul_ctxt->ctxt.force_writeback = 1;
>>>> hvmemul_ctxt->seg_reg_accessed = 0;
>>>> hvmemul_ctxt->seg_reg_dirty = 0;
>>>> - hvmemul_ctxt->set_context = 0;
>>>> + hvmemul_ctxt->set_context_data = 0;
>>>> + hvmemul_ctxt->set_context_insn = 0;
>>>> hvmemul_get_seg_reg(x86_seg_cs, hvmemul_ctxt);
>>>> hvmemul_get_seg_reg(x86_seg_ss, hvmemul_ctxt);
>>>> }
>>>> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
>>>> index ca96643..7462794 100644
>>>> --- a/xen/arch/x86/hvm/hvm.c
>>>> +++ b/xen/arch/x86/hvm/hvm.c
>>>> @@ -489,13 +489,16 @@ void hvm_do_resume(struct vcpu *v)
>>>>
>>>> if ( v->arch.vm_event->emulate_flags &
>>>> VM_EVENT_FLAG_SET_EMUL_READ_DATA )
>>>> - kind = EMUL_KIND_SET_CONTEXT;
>>>> + kind = EMUL_KIND_SET_CONTEXT_DATA;
>>>> else if ( v->arch.vm_event->emulate_flags &
>>>> VM_EVENT_FLAG_EMULATE_NOWRITE )
>>>> kind = EMUL_KIND_NOWRITE;
>>>> + else if ( v->arch.vm_event->emulate_flags &
>>>> + VM_EVENT_FLAG_SET_EMUL_INSN_DATA )
>>>> + kind = EMUL_KIND_SET_CONTEXT_INSN;
>>>>
>>>> - hvm_mem_access_emulate_one(kind, TRAP_invalid_op,
>>>> - HVM_DELIVER_NO_ERROR_CODE);
>>>> + hvm_emulate_one_vm_event(kind, TRAP_invalid_op,
>>>> + HVM_DELIVER_NO_ERROR_CODE);
>>>>
>>>> v->arch.vm_event->emulate_flags = 0;
>>>> }
>>>> diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c
>>>> index 2759e6f..d214716 100644
>>>> --- a/xen/arch/x86/hvm/vmx/vmx.c
>>>> +++ b/xen/arch/x86/hvm/vmx/vmx.c
>>>> @@ -57,6 +57,7 @@
>>>> #include <asm/altp2m.h>
>>>> #include <asm/event.h>
>>>> #include <asm/monitor.h>
>>>> +#include <asm/vm_event.h>
>>>> #include <public/arch-x86/cpuid.h>
>>>>
>>>> static bool_t __initdata opt_force_ept;
>>>> diff --git a/xen/arch/x86/vm_event.c b/xen/arch/x86/vm_event.c
>>>> index 343b9c8..03beed3 100644
>>>> --- a/xen/arch/x86/vm_event.c
>>>> +++ b/xen/arch/x86/vm_event.c
>>>> @@ -209,11 +209,18 @@ void vm_event_emulate_check(struct vcpu *v,
>>>> vm_event_response_t *rsp)
>>>> if ( p2m_mem_access_emulate_check(v, rsp) )
>>>> {
>>>> if ( rsp->flags & VM_EVENT_FLAG_SET_EMUL_READ_DATA )
>>>> - v->arch.vm_event->emul_read_data =
>>>> rsp->data.emul_read_data;
>>>> + v->arch.vm_event->emul_read = rsp->data.emul.read;
>>>>
>>>> v->arch.vm_event->emulate_flags = rsp->flags;
>>>> }
>>>> break;
>>>> + case VM_EVENT_REASON_SOFTWARE_BREAKPOINT:
>>>> + if ( rsp->flags & VM_EVENT_FLAG_SET_EMUL_INSN_DATA )
>>>> + {
>>>> + v->arch.vm_event->emul_insn = rsp->data.emul.insn;
>>>> + v->arch.vm_event->emulate_flags = rsp->flags;
>>>> + }
>>>> + break;
>>>> default:
>>>> break;
>>>> };
>>>> diff --git a/xen/common/vm_event.c b/xen/common/vm_event.c
>>>> index 907ab40..d8ee7f3 100644
>>>> --- a/xen/common/vm_event.c
>>>> +++ b/xen/common/vm_event.c
>>>> @@ -398,7 +398,6 @@ void vm_event_resume(struct domain *d, struct
>>>> vm_event_domain *ved)
>>>> * In some cases the response type needs extra handling, so here
>>>> * we call the appropriate handlers.
>>>> */
>>>> -
>>>> /* Check flags which apply only when the vCPU is paused */
>>>> if ( atomic_read(&v->vm_event_pause_count) )
>>>> {
>>>> diff --git a/xen/include/asm-x86/hvm/emulate.h
>>>> b/xen/include/asm-x86/hvm/emulate.h
>>>> index 3aabcbe..b52f99e 100644
>>>> --- a/xen/include/asm-x86/hvm/emulate.h
>>>> +++ b/xen/include/asm-x86/hvm/emulate.h
>>>> @@ -34,20 +34,22 @@ struct hvm_emulate_ctxt {
>>>>
>>>> uint32_t intr_shadow;
>>>>
>>>> - bool_t set_context;
>>>> + bool_t set_context_data;
>>>> + bool_t set_context_insn;
>>>> };
>>>>
>>>> enum emul_kind {
>>>> EMUL_KIND_NORMAL,
>>>> EMUL_KIND_NOWRITE,
>>>> - EMUL_KIND_SET_CONTEXT
>>>> + EMUL_KIND_SET_CONTEXT_DATA,
>>>> + EMUL_KIND_SET_CONTEXT_INSN
>>>
>>> Since this breaks compilation of existing clients, I think we should
>>> increment some macro to alow for compile-time switching (maybe
>>> VM_EVENT_INTERFACE_VERSION?).
>>
>> I'm not sure I follow - this is a Xen internal-only enumeration. What
>> kind-of clients are you referring to?
>
> Nevermind, I thought these changes propagate to the toolstack headers.
> Sorry for the confusion.
On second thought (and a night's rest), the problem is real. I've made
it a point to test the patches today before re-reviewing them, and this
happened:
bdvmixeneventmanager.cpp:359:46: error: ‘union vm_event_st::<anonymous>’
has no member named ‘emul_read_data’
uint32_t rspDataSize = sizeof( rsp.data.emul_read_data.data );
^
bdvmixeneventmanager.cpp:386:44: error: ‘union vm_event_st::<anonymous>’
has no member named ‘emul_read_data’
action, rsp.data.emul_read_data.data,
rspDataSize,
^
bdvmixeneventmanager.cpp:389:16: error: ‘union vm_event_st::<anonymous>’
has no member named ‘emul_read_data’
rsp.data.emul_read_data.size = rspDataSize;
^
make: *** [bdvmixeneventmanager.o] Error 1
So, as you can see, existing clients really don't compile without
modification.
Thanks,
Razvan
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