From 283c95d0e3891b64087706b344a4b545d04a6e62 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Radim=20Kr=C4=8Dm=C3=A1=C5=99?= Date: Wed, 9 Nov 2016 19:07:06 +0100 Subject: [PATCH] KVM: x86: emulate FXSAVE and FXRSTOR MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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: Radim Krčmář --- arch/x86/kvm/emulate.c | 129 ++++++++++++++++++++++++++++++++++++++++- 1 file changed, 128 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 6af3cac6ec89..7d4f9b7f06ee 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -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, } };