[3.13.y.z extended stable] Patch "KVM: x86: Emulator does not decode clflush well" has been added to staging queue

[Luis Henriques]

On Fri, Oct 31, 2014 at 01:53:45PM -0700, Kamal Mostafa wrote:
> This is a note to let you know that I have just added a patch titled
> 
>     KVM: x86: Emulator does not decode clflush well
> 
> to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
> which can be found at:
> 
>  http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue
> 
> This patch is scheduled to be released in version 3.13.11.11.
> 
> If you, or anyone else, feels it should not be added to this tree, please 
> reply to this email.
> 
> For more information about the 3.13.y.z tree, see
> https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
> 
> Thanks.
> -Kamal
> 
> ------
> 
> From 3cf1cc997f89242c852dca2469ca4303348d29a5 Mon Sep 17 00:00:00 2001
> From: Nadav Amit <namit at cs.technion.ac.il>
> Date: Mon, 13 Oct 2014 13:04:13 +0300
> Subject: KVM: x86: Emulator does not decode clflush well
> 
> commit 13e457e0eebf0a0c82c38ceb890d93eb826d62a6 upstream.
> 
> Currently, all group15 instructions are decoded as clflush (e.g., mfence,
> xsave).  In addition, the clflush instruction requires no prefix (66/f2/f3)
> would exist. If prefix exists it may encode a different instruction (e.g.,
> clflushopt).
> 
> Creating a group for clflush, and different group for each prefix.
> 
> This has been the case forever, but the next patch needs the cflush group
> in order to fix a bug introduced in 3.17.

Given the above ^^^

> Fixes: 41061cdb98a0bec464278b4db8e894a3121671f5

And the fact that this commit isn't present in 3.13, I'm not sure this
patch is relevant for this stable kernel.  Could someone confirm this
please?

Cheers,
--
Luís

> Signed-off-by: Nadav Amit <namit at cs.technion.ac.il>
> Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
> Signed-off-by: Kamal Mostafa <kamal at canonical.com>
> ---
>  arch/x86/kvm/emulate.c | 20 +++++++++++++++++---
>  1 file changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> index 38d3751..ed2db60 100644
> --- a/arch/x86/kvm/emulate.c
> +++ b/arch/x86/kvm/emulate.c
> @@ -3375,6 +3375,12 @@ static int em_bswap(struct x86_emulate_ctxt *ctxt)
>  	return X86EMUL_CONTINUE;
>  }
> 
> +static int em_clflush(struct x86_emulate_ctxt *ctxt)
> +{
> +	/* emulating clflush regardless of cpuid */
> +	return X86EMUL_CONTINUE;
> +}
> +
>  static bool valid_cr(int nr)
>  {
>  	switch (nr) {
> @@ -3711,6 +3717,16 @@ static const struct opcode group11[] = {
>  	X7(D(Undefined)),
>  };
> 
> +static const struct gprefix pfx_0f_ae_7 = {
> +	I(0, em_clflush), N, N, N,
> +};
> +
> +static const struct group_dual group15 = { {
> +	N, N, N, N, N, N, N, GP(0, &pfx_0f_ae_7),
> +}, {
> +	N, N, N, N, N, N, N, N,
> +} };
> +
>  static const struct gprefix pfx_0f_6f_0f_7f = {
>  	I(Mmx, em_mov), I(Sse | Aligned, em_mov), N, I(Sse | Unaligned, em_mov),
>  };
> @@ -3962,7 +3978,7 @@ static const struct opcode twobyte_table[256] = {
>  	F(DstMem | SrcReg | ModRM | BitOp | Lock | PageTable, em_bts),
>  	F(DstMem | SrcReg | Src2ImmByte | ModRM, em_shrd),
>  	F(DstMem | SrcReg | Src2CL | ModRM, em_shrd),
> -	D(ModRM), F(DstReg | SrcMem | ModRM, em_imul),
> +	GD(0, &group15), F(DstReg | SrcMem | ModRM, em_imul),
>  	/* 0xB0 - 0xB7 */
>  	I2bv(DstMem | SrcReg | ModRM | Lock | PageTable, em_cmpxchg),
>  	I(DstReg | SrcMemFAddr | ModRM | Src2SS, em_lseg),
> @@ -4838,8 +4854,6 @@ twobyte_insn:
>  	case 0x90 ... 0x9f:     /* setcc r/m8 */
>  		ctxt->dst.val = test_cc(ctxt->b, ctxt->eflags);
>  		break;
> -	case 0xae:              /* clflush */
> -		break;
>  	case 0xb6 ... 0xb7:	/* movzx */
>  		ctxt->dst.bytes = ctxt->op_bytes;
>  		ctxt->dst.val = (ctxt->src.bytes == 1) ? (u8) ctxt->src.val
> --
> 1.9.1
> 
> 
> -- 
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