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KVM: x86: emulate FXSAVE and FXRSTOR

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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 <rkrcmar@redhat.com>
This commit is contained in:
Radim Krčmář 2016-11-09 19:07:06 +01:00
parent aabba3c6ab
commit 283c95d0e3
1 changed files with 128 additions and 1 deletions
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129
arch/x86/kvm/emulate.c
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@ -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,
} };