Re: [RFC PATCH] emulator: Fix task switch into/out of VM86

[Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>]

(2012/01/10 5:10), Kevin Wolf wrote:

> @@ -2254,7 +2258,14 @@ static int load_state_from_tss32(struct x86_emulate_ctxt *ctxt,
>   	if (ctxt->ops->set_cr(ctxt, 3, tss->cr3))
>   		return emulate_gp(ctxt, 0);
>   	ctxt->_eip = tss->eip;
> +
>   	ctxt->eflags = tss->eflags | 2;

(Though not directly related to this RFC ...)

What is this 2 for?
Do we need to set a reserved bit?

> +	if (ctxt->eflags & 0x20000)

You can use a macro to indicate the flag.

1. from arch/x86/kvm/emulate.c:

/* EFLAGS bit definitions. */
#define EFLG_ID (1<<21)
#define EFLG_VIP (1<<20)
#define EFLG_VIF (1<<19)
#define EFLG_AC (1<<18)
#define EFLG_VM (1<<17)
#define EFLG_RF (1<<16)
...

#define EFLG_RESERVED_ZEROS_MASK 0xffc0802a
#define EFLG_RESERVED_ONE_MASK 2

2. from arch/x86/include/asm/processor-flags.h

/*
 * EFLAGS bits
 */
#define X86_EFLAGS_CF   0x00000001 /* Carry Flag */
#define X86_EFLAGS_PF   0x00000004 /* Parity Flag */
...
#define X86_EFLAGS_VM   0x00020000 /* Virtual Mode */
#define X86_EFLAGS_AC   0x00040000 /* Alignment Check */
#define X86_EFLAGS_VIF  0x00080000 /* Virtual Interrupt Flag */
#define X86_EFLAGS_VIP  0x00100000 /* Virtual Interrupt Pending */
#define X86_EFLAGS_ID   0x00200000 /* CPUID detection flag */


Two possibilities, not nice, but both are used in emulate.c.

	Takuya