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Commit 283c95d0 authored by Radim Krčmář's avatar Radim Krčmář
Browse files

KVM: x86: emulate FXSAVE and FXRSTOR 



Internal errors were reported on 16 bit fxsave and fxrstor with ipxe.
Old Intels don't have unrestricted_guest, so we have to emulate them.

The patch takes advantage of the hardware implementation.

AMD and Intel differ in saving and restoring other fields in first 32
bytes.  A test wrote 0xff to the fxsave area, 0 to upper bits of MCSXR
in the fxsave area, executed fxrstor, rewrote the fxsave area to 0xee,
and executed fxsave:

  Intel (Nehalem):
    7f 1f 7f 7f ff 00 ff 07 ff ff ff ff ff ff 00 00
    ff ff ff ff ff ff 00 00 ff ff 00 00 ff ff 00 00
  Intel (Haswell -- deprecated FPU CS and FPU DS):
    7f 1f 7f 7f ff 00 ff 07 ff ff ff ff 00 00 00 00
    ff ff ff ff 00 00 00 00 ff ff 00 00 ff ff 00 00
  AMD (Opteron 2300-series):
    7f 1f 7f 7f ff 00 ee ee ee ee ee ee ee ee ee ee
    ee ee ee ee ee ee ee ee ff ff 00 00 ff ff 02 00

fxsave/fxrstor will only be emulated on early Intels, so KVM can't do
much to improve the situation.

Signed-off-by: default avatarRadim Krčmář <rkrcmar@redhat.com>
parent aabba3c6

arch/x86/kvm/emulate.c

+128 −1
Original line number Diff line number Diff line
@@ -3883,6 +3883,131 @@ static int em_movsxd(struct x86_emulate_ctxt *ctxt) 
	return X86EMUL_CONTINUE;

}



static int check_fxsr(struct x86_emulate_ctxt *ctxt)

{

	u32 eax = 1, ebx, ecx = 0, edx;



	ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx);

	if (!(edx & FFL(FXSR)))

		return emulate_ud(ctxt);



	if (ctxt->ops->get_cr(ctxt, 0) & (X86_CR0_TS | X86_CR0_EM))

		return emulate_nm(ctxt);



	/*

	 * Don't emulate a case that should never be hit, instead of working

	 * around a lack of fxsave64/fxrstor64 on old compilers.

	 */

	if (ctxt->mode >= X86EMUL_MODE_PROT64)

		return X86EMUL_UNHANDLEABLE;



	return X86EMUL_CONTINUE;

}



/*

 * FXSAVE and FXRSTOR have 4 different formats depending on execution mode,

 *  1) 16 bit mode

 *  2) 32 bit mode

 *     - like (1), but FIP and FDP (foo) are only 16 bit.  At least Intel CPUs

 *       preserve whole 32 bit values, though, so (1) and (2) are the same wrt.

 *       save and restore

 *  3) 64-bit mode with REX.W prefix

 *     - like (2), but XMM 8-15 are being saved and restored

 *  4) 64-bit mode without REX.W prefix

 *     - like (3), but FIP and FDP are 64 bit

 *

 * Emulation uses (3) for (1) and (2) and preserves XMM 8-15 to reach the

 * desired result.  (4) is not emulated.

 *

 * Note: Guest and host CPUID.(EAX=07H,ECX=0H):EBX[bit 13] (deprecate FPU CS

 * and FPU DS) should match.

 */

static int em_fxsave(struct x86_emulate_ctxt *ctxt)

{

	struct fxregs_state fx_state;

	size_t size;

	int rc;



	rc = check_fxsr(ctxt);

	if (rc != X86EMUL_CONTINUE)

		return rc;



	ctxt->ops->get_fpu(ctxt);



	rc = asm_safe("fxsave %[fx]", , [fx] "+m"(fx_state));



	ctxt->ops->put_fpu(ctxt);



	if (rc != X86EMUL_CONTINUE)

		return rc;



	if (ctxt->ops->get_cr(ctxt, 4) & X86_CR4_OSFXSR)

		size = offsetof(struct fxregs_state, xmm_space[8 * 16/4]);

	else

		size = offsetof(struct fxregs_state, xmm_space[0]);



	return segmented_write(ctxt, ctxt->memop.addr.mem, &fx_state, size);

}



static int fxrstor_fixup(struct x86_emulate_ctxt *ctxt,

		struct fxregs_state *new)

{

	int rc = X86EMUL_CONTINUE;

	struct fxregs_state old;



	rc = asm_safe("fxsave %[fx]", , [fx] "+m"(old));

	if (rc != X86EMUL_CONTINUE)

		return rc;



	/*

	 * 64 bit host will restore XMM 8-15, which is not correct on non-64

	 * bit guests.  Load the current values in order to preserve 64 bit

	 * XMMs after fxrstor.

	 */

#ifdef CONFIG_X86_64

	/* XXX: accessing XMM 8-15 very awkwardly */

	memcpy(&new->xmm_space[8 * 16/4], &old.xmm_space[8 * 16/4], 8 * 16);

#endif



	/*

	 * Hardware doesn't save and restore XMM 0-7 without CR4.OSFXSR, but

	 * does save and restore MXCSR.

	 */

	if (!(ctxt->ops->get_cr(ctxt, 4) & X86_CR4_OSFXSR))

		memcpy(new->xmm_space, old.xmm_space, 8 * 16);



	return rc;

}



static int em_fxrstor(struct x86_emulate_ctxt *ctxt)

{

	struct fxregs_state fx_state;

	int rc;



	rc = check_fxsr(ctxt);

	if (rc != X86EMUL_CONTINUE)

		return rc;



	rc = segmented_read(ctxt, ctxt->memop.addr.mem, &fx_state, 512);

	if (rc != X86EMUL_CONTINUE)

		return rc;



	if (fx_state.mxcsr >> 16)

		return emulate_gp(ctxt, 0);



	ctxt->ops->get_fpu(ctxt);



	if (ctxt->mode < X86EMUL_MODE_PROT64)

		rc = fxrstor_fixup(ctxt, &fx_state);



	if (rc == X86EMUL_CONTINUE)

		rc = asm_safe("fxrstor %[fx]", : [fx] "m"(fx_state));



	ctxt->ops->put_fpu(ctxt);



	return rc;

}



static bool valid_cr(int nr)

{

	switch (nr) {
@@ -4235,7 +4360,9 @@ static const struct gprefix pfx_0f_ae_7 = { 
};



static const struct group_dual group15 = { {

	N, N, N, N, N, N, N, GP(0, &pfx_0f_ae_7),

	I(ModRM | Aligned16, em_fxsave),

	I(ModRM | Aligned16, em_fxrstor),

	N, N, N, N, N, GP(0, &pfx_0f_ae_7),

}, {

	N, N, N, N, N, N, N, N,

} };