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Date: Wed, 30 Oct 2013 18:56:10 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Borislav Petkov <bp@...en8.de>
CC: Gleb Natapov <gleb@...hat.com>,
LKML <linux-kernel@...r.kernel.org>,
Borislav Petkov <bp@...e.de>, "H. Peter Anvin" <hpa@...or.com>,
Andre Przywara <andre@...rep.de>,
Joerg Roedel <joro@...tes.org>, X86 ML <x86@...nel.org>,
KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH 5/5 -v3.1] kvm: Emulate MOVBE
Il 29/10/2013 12:54, Borislav Petkov ha scritto:
> From: Borislav Petkov <bp@...e.de>
>
> This basically came from the need to be able to boot 32-bit Atom SMP
> guests on an AMD host, i.e. a host which doesn't support MOVBE. As a
> matter of fact, qemu has since recently received MOVBE support but we
> cannot share that with kvm emulation and thus we have to do this in the
> host. We're waay faster in kvm anyway. :-)
>
> So, we piggyback on the #UD path and emulate the MOVBE functionality.
> With it, an 8-core SMP guest boots in under 6 seconds.
>
> Also, requesting MOVBE emulation needs to happen explicitly to work,
> i.e. qemu -cpu n270,+movbe...
>
> Just FYI, a fairly straight-forward boot of a MOVBE-enabled 3.9-rc6+
> kernel in kvm executes MOVBE ~60K times.
>
> Signed-off-by: Andre Przywara <andre@...rep.de>
> Signed-off-by: Borislav Petkov <bp@...e.de>
> ---
> arch/x86/kvm/cpuid.c | 18 ++++++++++++++++-
> arch/x86/kvm/emulate.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++----
> 2 files changed, 66 insertions(+), 5 deletions(-)
Thanks, I've applied these patches to kvm/queue.
Paolo
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 78a4439bfdc5..86d5756dda07 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -222,6 +222,22 @@ static bool supported_xcr0_bit(unsigned bit)
> static int __do_cpuid_ent_emulated(struct kvm_cpuid_entry2 *entry,
> u32 func, u32 index, int *nent, int maxnent)
> {
> + switch (func) {
> + case 0:
> + entry->eax = 1; /* only one leaf currently */
> + ++*nent;
> + break;
> + case 1:
> + entry->ecx = F(MOVBE);
> + ++*nent;
> + break;
> + default:
> + break;
> + }
> +
> + entry->function = func;
> + entry->index = index;
> +
> return 0;
> }
>
> @@ -593,7 +609,7 @@ int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,
> return -EINVAL;
>
> r = -ENOMEM;
> - cpuid_entries = vmalloc(sizeof(struct kvm_cpuid_entry2) * cpuid->nent);
> + cpuid_entries = vzalloc(sizeof(struct kvm_cpuid_entry2) * cpuid->nent);
> if (!cpuid_entries)
> goto out;
>
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 6c5cfe962b28..8e2a07bd8eac 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -2961,6 +2961,46 @@ static int em_mov(struct x86_emulate_ctxt *ctxt)
> return X86EMUL_CONTINUE;
> }
>
> +#define FFL(x) bit(X86_FEATURE_##x)
> +
> +static int em_movbe(struct x86_emulate_ctxt *ctxt)
> +{
> + u32 ebx, ecx, edx, eax = 1;
> + u16 tmp;
> +
> + /*
> + * Check MOVBE is set in the guest-visible CPUID leaf.
> + */
> + ctxt->ops->get_cpuid(ctxt, &eax, &ebx, &ecx, &edx);
> + if (!(ecx & FFL(MOVBE)))
> + return emulate_ud(ctxt);
> +
> + switch (ctxt->op_bytes) {
> + case 2:
> + /*
> + * From MOVBE definition: "...When the operand size is 16 bits,
> + * the upper word of the destination register remains unchanged
> + * ..."
> + *
> + * Both casting ->valptr and ->val to u16 breaks strict aliasing
> + * rules so we have to do the operation almost per hand.
> + */
> + tmp = (u16)ctxt->src.val;
> + ctxt->dst.val &= ~0xffffUL;
> + ctxt->dst.val |= (unsigned long)swab16(tmp);
> + break;
> + case 4:
> + ctxt->dst.val = swab32((u32)ctxt->src.val);
> + break;
> + case 8:
> + ctxt->dst.val = swab64(ctxt->src.val);
> + break;
> + default:
> + return X86EMUL_PROPAGATE_FAULT;
> + }
> + return X86EMUL_CONTINUE;
> +}
> +
> static int em_cr_write(struct x86_emulate_ctxt *ctxt)
> {
> if (ctxt->ops->set_cr(ctxt, ctxt->modrm_reg, ctxt->src.val))
> @@ -3893,11 +3933,11 @@ static const struct opcode twobyte_table[256] = {
> };
>
> static const struct gprefix three_byte_0f_38_f0 = {
> - N, N, N, N
> + I(DstReg | SrcMem | Mov, em_movbe), N, N, N
> };
>
> static const struct gprefix three_byte_0f_38_f1 = {
> - N, N, N, N
> + I(DstMem | SrcReg | Mov, em_movbe), N, N, N
> };
>
> /*
> @@ -3907,8 +3947,13 @@ static const struct gprefix three_byte_0f_38_f1 = {
> static const struct opcode opcode_map_0f_38[256] = {
> /* 0x00 - 0x7f */
> X16(N), X16(N), X16(N), X16(N), X16(N), X16(N), X16(N), X16(N),
> - /* 0x80 - 0xff */
> - X16(N), X16(N), X16(N), X16(N), X16(N), X16(N), X16(N), X16(N)
> + /* 0x80 - 0xef */
> + X16(N), X16(N), X16(N), X16(N), X16(N), X16(N), X16(N),
> + /* 0xf0 - 0xf1 */
> + GP(EmulateOnUD | ModRM | Prefix, &three_byte_0f_38_f0),
> + GP(EmulateOnUD | ModRM | Prefix, &three_byte_0f_38_f1),
> + /* 0xf2 - 0xff */
> + N, N, X4(N), X8(N)
> };
>
> #undef D
>
--
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