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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 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?
Tamas
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