Re: [patch] VMX Unrestricted mode support

[Jan Kiszka <jan.kiszka@siemens.com>]

Nitin A Kamble wrote:
> Hi Avi,
>   I find that the qemu processor reset state is not per the IA32
> processor specifications. (Sections 8.1.1 of
> http://www.intel.com/Assets/PDF/manual/253668.pdf)
> 
> In qemu-kvm.git in file target-i386/helper.c in function cpu_reset the
> segment registers are initialized as follows:
> 
> cpu_x86_load_seg_cache(env, R_CS, 0xf000, 0xffff0000, 0xffff,
>                            DESC_P_MASK | DESC_S_MASK | DESC_CS_MASK | 
> 				DESC_R_MASK);
> cpu_x86_load_seg_cache(env, R_DS, 0, 0, 0xffff,
>                            DESC_P_MASK | DESC_S_MASK | DESC_W_MASK);
> cpu_x86_load_seg_cache(env, R_ES, 0, 0, 0xffff,
>                            DESC_P_MASK | DESC_S_MASK | DESC_W_MASK);
> cpu_x86_load_seg_cache(env, R_SS, 0, 0, 0xffff,
>                            DESC_P_MASK | DESC_S_MASK | DESC_W_MASK);
> cpu_x86_load_seg_cache(env, R_FS, 0, 0, 0xffff,
>                            DESC_P_MASK | DESC_S_MASK | DESC_W_MASK);
> cpu_x86_load_seg_cache(env, R_GS, 0, 0, 0xffff,
>                            DESC_P_MASK | DESC_S_MASK | DESC_W_MASK);
> 
> While the IA32 cpu reset state specification says that Segment Accessed
> bit is also 1 at the time of cpu reset. so the above code should look
> like this:
> 
> cpu_x86_load_seg_cache(env, R_CS, 0xf000, 0xffff0000, 0xffff,
>                  DESC_P_MASK | DESC_S_MASK | DESC_CS_MASK | 
>                  DESC_R_MASK | DESC_A_MASK);
> cpu_x86_load_seg_cache(env, R_DS, 0, 0, 0xffff,
>                  DESC_P_MASK | DESC_S_MASK | DESC_W_MASK | DESC_A_MASK);
> cpu_x86_load_seg_cache(env, R_ES, 0, 0, 0xffff,
>                  DESC_P_MASK | DESC_S_MASK | DESC_W_MASK| DESC_A_MASK);
> cpu_x86_load_seg_cache(env, R_SS, 0, 0, 0xffff,
>                  DESC_P_MASK | DESC_S_MASK | DESC_W_MASK |DESC_A_MASK);
> cpu_x86_load_seg_cache(env, R_FS, 0, 0, 0xffff,
>                  DESC_P_MASK | DESC_S_MASK | DESC_W_MASK);
> cpu_x86_load_seg_cache(env, R_GS, 0, 0, 0xffff,
>                  DESC_P_MASK | DESC_S_MASK | DESC_W_MASK);
> 
> This discrepancy is adding the need of the following function in the
> unrestricted guest patch.

As Avi already indicated: Independent of the kvm workaround for older
qemu versions, please post (to qemu-devel) a patch against upstream's
git to fix the discrepancy.

Jan

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