[PATCH] RE: ia32 emulation on Intel CPU

[PATCH] RE: ia32 emulation on Intel CPU

[Kiselev, Sergey]

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Following patch adds back this functionality:
 
Signed-off-by: Sergey Kiselev <sergey.kiselev-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>

--- kvm-18.orig/qemu/qemu-kvm.c	2007-03-21 17:55:11.000000000 +0200
+++ kvm-18/qemu/qemu-kvm.c	2007-03-25 20:42:53.000000000 +0200
@@ -693,6 +693,37 @@
 	if ((h_edx & 0x00100000) == 0)
 	    e->edx &= ~0x00100000u;
     }
+    // sysenter isn't supported on compatibility mode on AMD.  and
syscall
+    // isn't supported in compatibility mode on Intel.  so advertise
the
+    // actuall cpu, and say goodbye to migration between different
vendors
+    // is you use compatibility mode.
+    if (function == 0) {
+	uint32_t bcd[3];
+	asm (
+#ifdef __x86_64__
+	     "push %%rax; push %%rbx; push %%rcx; push %%rdx \n\t"
+	     "mov $0, %%eax \n\t"
+	     "cpuid \n\t"
+	     "mov (%%rsp), %%rax \n\t"
+	     "mov %%ebx, (%%rax) \n\t"
+	     "mov %%ecx, 4(%%rax) \n\t"
+	     "mov %%edx, 8(%%rax) \n\t"
+	     "pop %%rdx; pop %%rcx; pop %%rbx; pop %%rax"
+#else
+	     "push %%eax; push %%ebx; push %%ecx; push %%edx \n\t"
+	     "mov $0, %%eax \n\t"
+	     "cpuid \n\t"
+	     "mov (%%esp), %%eax \n\t"
+	     "mov %%ebx, (%%eax) \n\t"
+	     "mov %%ecx, 4(%%eax) \n\t"
+	     "mov %%edx, 8(%%eax) \n\t"
+	     "pop %%edx; pop %%ecx; pop %%ebx; pop %%eax"
+#endif
+	     : : "d"(bcd) : "memory");
+	e->ebx = bcd[0];
+	e->ecx = bcd[1];
+	e->edx = bcd[2];
+    }
 }
 
 int kvm_qemu_init_env(CPUState *cenv)



________________________________

From: Kiselev, Sergey 
Sent: 25 March 2007 20:28
To: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
Subject: ia32 emulation on Intel CPU


Hi,
 
In kvm-18 code that returned actual CPU vendor string was removed from
qemu-kvm.c (so kvm-18 running on Intel's CPU will return "AuthenticAMD"
vendor string).
Linux uses boot_cpu_data.x86_vendor (derived from vendor string) to
determine whenever to use syscall or sysenter instruction. It seems that
when running under kvm it will always try to use sysenter, which causes
invalid instruction trap...
 
Thanks,
Sergey

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Signed-off-by: Sergey Kiselev <sergey.kiselev@intel.com>

--- kvm-18.orig/qemu/qemu-kvm.c	2007-03-21 17:55:11.000000000 +0200
+++ kvm-18/qemu/qemu-kvm.c	2007-03-25 20:42:53.000000000 +0200
@@ -693,6 +693,37 @@
 	if ((h_edx & 0x00100000) == 0)
 	    e->edx &= ~0x00100000u;
     }
+    // sysenter isn't supported on compatibility mode on AMD.  and syscall
+    // isn't supported in compatibility mode on Intel.  so advertise the
+    // actuall cpu, and say goodbye to migration between different vendors
+    // is you use compatibility mode.
+    if (function == 0) {
+	uint32_t bcd[3];
+	asm (
+#ifdef __x86_64__
+	     "push %%rax; push %%rbx; push %%rcx; push %%rdx \n\t"
+	     "mov $0, %%eax \n\t"
+	     "cpuid \n\t"
+	     "mov (%%rsp), %%rax \n\t"
+	     "mov %%ebx, (%%rax) \n\t"
+	     "mov %%ecx, 4(%%rax) \n\t"
+	     "mov %%edx, 8(%%rax) \n\t"
+	     "pop %%rdx; pop %%rcx; pop %%rbx; pop %%rax"
+#else
+	     "push %%eax; push %%ebx; push %%ecx; push %%edx \n\t"
+	     "mov $0, %%eax \n\t"
+	     "cpuid \n\t"
+	     "mov (%%esp), %%eax \n\t"
+	     "mov %%ebx, (%%eax) \n\t"
+	     "mov %%ecx, 4(%%eax) \n\t"
+	     "mov %%edx, 8(%%eax) \n\t"
+	     "pop %%edx; pop %%ecx; pop %%ebx; pop %%eax"
+#endif
+	     : : "d"(bcd) : "memory");
+	e->ebx = bcd[0];
+	e->ecx = bcd[1];
+	e->edx = bcd[2];
+    }
 }
 
 int kvm_qemu_init_env(CPUState *cenv)

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Re: [PATCH] RE: ia32 emulation on Intel CPU

[Avi Kivity]

Kiselev, Sergey wrote:
> Following patch adds back this functionality:
>  
> Signed-off-by: Sergey Kiselev <sergey.kiselev-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
>   

Applied, thanks.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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