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[Xen-devel] [PATCH RFC V11 5/5] xen: Handle resumed instruction based on previous mem_event reply

From: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>

Date: Tue, 2 Sep 2014 18:37:19 +0300

Cc: kevin.tian@xxxxxxxxx, ian.campbell@xxxxxxxxxx, Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>, stefano.stabellini@xxxxxxxxxxxxx, jun.nakajima@xxxxxxxxx, andrew.cooper3@xxxxxxxxxx, eddie.dong@xxxxxxxxx, tim@xxxxxxx, JBeulich@xxxxxxxx, ian.jackson@xxxxxxxxxxxxx

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List-id: Xen developer discussion <xen-devel.lists.xen.org>

In a scenario where a page fault that triggered a mem_event occured, p2m_mem_access_check() will now be able to either 1) emulate the current instruction, or 2) emulate it, but don't allow it to perform any writes. Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx> --- Changes since V10: - Removed #ifndef NDEBUG. Changes since V9: - Changed the EXIT_REASON_EPT_VIOLATION check into an ASSERT(). Changes since V8: - Make sure that the exit reason is EXIT_REASON_EPT_VIOLATION before checking for EPT_GLA_FAULT. Changes since V7: - Now calling hvm_mem_event_emulate_one() instead of hvm_emulate_one_full() (renamed in the first patch). Changes since V5: - Fixed indentation. - Re-ordered a set of if() conditions. Changes since V4: - Renamed "exited_by_pagefault" to "exited_by_nested_pagefault". - Folded two long lines. - Combined two "if" statements. - Moved "violation = 0;" to the XENMEM_access_rwx case. Changes since V3: - Collapsed verbose lines into a single "else if()". - Changed an int to bool_t. - Fixed a minor coding style issue. - Now computing the first parameter to hvm_emulate_one_full() (replaced an "if" with a single call). - Added code comments about eip and gla reset (clarity issue). - Removed duplicate code by Andrew Cooper (introduced in V2, since committed). Changes since V2: - Moved the __vmread(EXIT_QUALIFICATION, &exit_qualification); code in vmx.c, accessible via hvm_funcs. - Incorporated changes by Andrew Cooper ("[PATCH 1/2] Xen/mem_event: Validate the response vcpu_id before acting on it." Changes since V1: - Removed the 'skip' code which required computing the current instruction length. - Removed the set_ad_bits() code that attempted to modify the 'accessed' and 'dirty' bits for instructions that the emulator can't handle at the moment. --- xen/arch/x86/domain.c | 3 ++ xen/arch/x86/hvm/vmx/vmx.c | 16 ++++++++ xen/arch/x86/mm/p2m.c | 84 ++++++++++++++++++++++++++++++++++++++++ xen/include/asm-x86/domain.h | 9 +++++ xen/include/asm-x86/hvm/hvm.h | 2 + xen/include/public/mem_event.h | 12 +++--- 6 files changed, 121 insertions(+), 5 deletions(-) diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c index f7e0e78..7b1dfe6 100644 --- a/xen/arch/x86/domain.c +++ b/xen/arch/x86/domain.c @@ -415,6 +415,9 @@ int vcpu_initialise(struct vcpu *v) v->arch.flags = TF_kernel_mode; + /* By default, do not emulate */ + v->arch.mem_event.emulate_flags = 0; + rc = mapcache_vcpu_init(v); if ( rc ) return rc; diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c index b08664e..cc317a4 100644 --- a/xen/arch/x86/hvm/vmx/vmx.c +++ b/xen/arch/x86/hvm/vmx/vmx.c @@ -1695,6 +1695,21 @@ static void vmx_enable_msr_exit_interception(struct domain *d) MSR_TYPE_W); } +static bool_t vmx_exited_by_nested_pagefault(void) +{ + unsigned long exit_qualification, exit_reason; + + __vmread(VM_EXIT_REASON, &exit_reason); + ASSERT(exit_reason == EXIT_REASON_EPT_VIOLATION); + + __vmread(EXIT_QUALIFICATION, &exit_qualification); + + if ( (exit_qualification & EPT_GLA_FAULT) == 0 ) + return 0; + + return 1; +} + static struct hvm_function_table __initdata vmx_function_table = { .name = "VMX", .cpu_up_prepare = vmx_cpu_up_prepare, @@ -1754,6 +1769,7 @@ static struct hvm_function_table __initdata vmx_function_table = { .nhvm_hap_walk_L1_p2m = nvmx_hap_walk_L1_p2m, .hypervisor_cpuid_leaf = vmx_hypervisor_cpuid_leaf, .enable_msr_exit_interception = vmx_enable_msr_exit_interception, + .exited_by_nested_pagefault = vmx_exited_by_nested_pagefault, }; const struct hvm_function_table * __init start_vmx(void) diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c index 6ed4109..3f35832 100644 --- a/xen/arch/x86/mm/p2m.c +++ b/xen/arch/x86/mm/p2m.c @@ -1391,6 +1391,7 @@ bool_t p2m_mem_access_check(paddr_t gpa, unsigned long gla, p2m_access_t p2ma; mem_event_request_t *req; int rc; + unsigned long eip = guest_cpu_user_regs()->eip; /* First, handle rx2rw conversion automatically. * These calls to p2m->set_entry() must succeed: we have the gfn @@ -1443,6 +1444,36 @@ bool_t p2m_mem_access_check(paddr_t gpa, unsigned long gla, return 1; } } + else if ( v->arch.mem_event.emulate_flags == 0 && + hvm_funcs.exited_by_nested_pagefault && + !hvm_funcs.exited_by_nested_pagefault() ) /* don't send a mem_event */ + { + v->arch.mem_event.emulate_flags = MEM_EVENT_FLAG_EMULATE; + v->arch.mem_event.gpa = gpa; + v->arch.mem_event.eip = eip; + } + + /* The previous mem_event reply does not match the current state. */ + if ( v->arch.mem_event.gpa != gpa || v->arch.mem_event.eip != eip ) + { + /* Don't emulate the current instruction, send a new mem_event. */ + v->arch.mem_event.emulate_flags = 0; + + /* Make sure to mark the current state to match it again against + * the new mem_event about to be sent. */ + v->arch.mem_event.gpa = gpa; + v->arch.mem_event.eip = eip; + } + + if ( v->arch.mem_event.emulate_flags ) + { + hvm_mem_event_emulate_one((v->arch.mem_event.emulate_flags & + MEM_EVENT_FLAG_EMULATE_NOWRITE) != 0, + TRAP_invalid_op, HVM_DELIVER_NO_ERROR_CODE); + + v->arch.mem_event.emulate_flags = 0; + return 1; + } *req_ptr = NULL; req = xzalloc(mem_event_request_t); @@ -1498,6 +1529,59 @@ void p2m_mem_access_resume(struct domain *d) v = d->vcpu[rsp.vcpu_id]; + /* Mark vcpu for skipping one instruction upon rescheduling */ + if ( rsp.flags & MEM_EVENT_FLAG_EMULATE ) + { + xenmem_access_t access; + bool_t violation = 1; + + v->arch.mem_event.emulate_flags = 0; + + if ( p2m_get_mem_access(d, rsp.gfn, &access) == 0 ) + { + switch ( access ) + { + case XENMEM_access_n: + case XENMEM_access_n2rwx: + default: + violation = rsp.access_r || rsp.access_w || rsp.access_x; + break; + + case XENMEM_access_r: + violation = rsp.access_w || rsp.access_x; + break; + + case XENMEM_access_w: + violation = rsp.access_r || rsp.access_x; + break; + + case XENMEM_access_x: + violation = rsp.access_r || rsp.access_w; + break; + + case XENMEM_access_rx: + case XENMEM_access_rx2rw: + violation = rsp.access_w; + break; + + case XENMEM_access_wx: + violation = rsp.access_r; + break; + + case XENMEM_access_rw: + violation = rsp.access_x; + break; + + case XENMEM_access_rwx: + violation = 0; + break; + } + } + + if ( violation ) + v->arch.mem_event.emulate_flags = rsp.flags; + } + /* Unpause domain */ if ( rsp.flags & MEM_EVENT_FLAG_VCPU_PAUSED ) mem_event_vcpu_unpause(v); diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h index 83329ed..440aa81 100644 --- a/xen/include/asm-x86/domain.h +++ b/xen/include/asm-x86/domain.h @@ -458,6 +458,15 @@ struct arch_vcpu /* A secondary copy of the vcpu time info. */ XEN_GUEST_HANDLE(vcpu_time_info_t) time_info_guest; + + /* Should we emulate the next matching instruction on VCPU resume + * after a mem_event? */ + struct { + uint32_t emulate_flags; + unsigned long gpa; + unsigned long eip; + } mem_event; + } __cacheline_aligned; smap_check_policy_t smap_policy_change(struct vcpu *v, diff --git a/xen/include/asm-x86/hvm/hvm.h b/xen/include/asm-x86/hvm/hvm.h index 3b0bde9..9ab126c 100644 --- a/xen/include/asm-x86/hvm/hvm.h +++ b/xen/include/asm-x86/hvm/hvm.h @@ -208,6 +208,8 @@ struct hvm_function_table { uint32_t *ecx, uint32_t *edx); void (*enable_msr_exit_interception)(struct domain *d); + + bool_t (*exited_by_nested_pagefault)(void); }; extern struct hvm_function_table hvm_funcs; diff --git a/xen/include/public/mem_event.h b/xen/include/public/mem_event.h index d3dd9c6..92c063c 100644 --- a/xen/include/public/mem_event.h +++ b/xen/include/public/mem_event.h @@ -31,11 +31,13 @@ #include "io/ring.h" /* Memory event flags */ -#define MEM_EVENT_FLAG_VCPU_PAUSED (1 << 0) -#define MEM_EVENT_FLAG_DROP_PAGE (1 << 1) -#define MEM_EVENT_FLAG_EVICT_FAIL (1 << 2) -#define MEM_EVENT_FLAG_FOREIGN (1 << 3) -#define MEM_EVENT_FLAG_DUMMY (1 << 4) +#define MEM_EVENT_FLAG_VCPU_PAUSED (1 << 0) +#define MEM_EVENT_FLAG_DROP_PAGE (1 << 1) +#define MEM_EVENT_FLAG_EVICT_FAIL (1 << 2) +#define MEM_EVENT_FLAG_FOREIGN (1 << 3) +#define MEM_EVENT_FLAG_DUMMY (1 << 4) +#define MEM_EVENT_FLAG_EMULATE (1 << 5) +#define MEM_EVENT_FLAG_EMULATE_NOWRITE (1 << 6) /* Reasons for the memory event request */ #define MEM_EVENT_REASON_UNKNOWN 0 /* typical reason */ -- 1.7.9.5 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel

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