[PATCH 0/3] KVM: x86: improve reexecute_instruction

[Xiao Guangrong]

The current reexecute_instruction can not well detect the failed instruction
emulation. It allows guest to retry all the instructions except it accesses
on error pfn.

For example, these cases can not be detected:
- for tdp used
  currently, it refused to retry all instructions. If nested npt is used, the
  emulation may be caused by shadow page, it can be fixed by unshadow the
  shadow page.

- for shadow mmu
  some cases are nested-write-protect, for example, if the page we want to
  write is used as PDE but it chains to itself. Under this case, we should
  stop the emulation and report the case to userspace.

This test case based on kvm-unit-test can trigger a infinite loop on current
code (ept = 0), after this patchset, it can report the error to Qemu.

Marcelo, I am afraid this test case can not be putted on kvm-unit-test,
autotest is confused about this case since it can abort Qemu.

Subject: [PATCH] access test: test unhandleable instruction

Test the instruction which can not be handled by kvm

Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
---
 x86/access.c |   27 ++++++++++++++++++++++++++-
 1 files changed, 26 insertions(+), 1 deletions(-)

diff --git a/x86/access.c b/x86/access.c
index 23a5995..e88db6b 100644
--- a/x86/access.c
+++ b/x86/access.c
@@ -2,6 +2,7 @@
 #include "libcflat.h"
 #include "desc.h"
 #include "processor.h"
+#include "vm.h"

 #define smp_id() 0

@@ -739,6 +740,28 @@ err:
 	return 0;
 }

+static int check_retry_unhandleable_ins(ac_pool_t *pool)
+{
+	unsigned long mem = 30 * 1024 * 1024;
+	unsigned long esp;
+	ac_test_t at;
+
+	ac_test_init(&at, (void *)(0x123406003000));
+	at.flags[AC_PDE_PRESENT] = at.flags[AC_PDE_WRITABLE] = 1;
+	at.flags[AC_PTE_PRESENT] = at.flags[AC_PTE_WRITABLE] = 1;
+	at.flags[AC_CPU_CR0_WP] = 1;
+
+	at.phys = mem;
+	ac_setup_specific_pages(&at, pool, mem, 0);
+
+	asm volatile("mov %%rsp, %%rax  \n\t" : "=a"(esp));
+	asm volatile("mov %%rax, %%rsp  \n\t" : : "a"(0x123406003000 + 0xf0));
+	asm volatile ("int $0x3 \n\t");
+	asm volatile("mov %%rax, %%rsp  \n\t" : : "a"(esp));
+
+	return 1;
+}
+
 int ac_test_exec(ac_test_t *at, ac_pool_t *pool)
 {
     int r;
@@ -756,7 +779,8 @@ const ac_test_fn ac_test_cases[] =
 {
 	corrupt_hugepage_triger,
 	check_pfec_on_prefetch_pte,
-	check_smep_andnot_wp
+	check_smep_andnot_wp,
+	check_retry_unhandleable_ins
 };

 int ac_test_run(void)
@@ -770,6 +794,7 @@ int ac_test_run(void)
     tests = successes = 0;
     ac_env_int(&pool);
     ac_test_init(&at, (void *)(0x123400000000 + 16 * smp_id()));
+
     do {
 	if (at.flags[AC_CPU_CR4_SMEP] && (ptl2[2] & 0x4))
 		ptl2[2] -= 0x4;
-- 
1.7.7.6

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