Re: [Xen-devel] [PATCH v3 03/24] x86/emul: Simplfy emulation state setup

[George Dunlap <George.Dunlap@xxxxxxxxxx>]

> On Nov 30, 2016, at 9:50 PM, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
> 
> The current code to set up emulation state is ad-hoc and error prone.
> 
> * Consistently zero all emulation state structures.
> * Avoid explicitly initialising some state to 0.
> * Explicitly identify all input and output state in x86_emulate_ctxt.  This
>   involves rearanging some fields.
> * Have x86_decode() explicitly initalise all output state at its start.
> 
> While making the above changes, two minor tweaks:
> 
> * Move the calculation of hvmemul_ctxt->ctxt.swint_emulate from
>   _hvm_emulate_one() to hvm_emulate_init_once().  It doesn't need
>   recalculating for each instruction.
> * Change force_writeback to being a boolean, to match its use.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Acked-by: Tim Deegan <tim@xxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

Not sure this is still needed, but just in case:

Acked-by: George Dunlap <george.dunlap@xxxxxxxxxx>

> ---
> CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> 
> v2:
> * Split x86_emulate_ctxt into three sections
> ---
> xen/arch/x86/hvm/emulate.c             | 28 +++++++++++++++-------------
> xen/arch/x86/mm.c                      | 14 ++++++++------
> xen/arch/x86/mm/shadow/common.c        |  4 ++--
> xen/arch/x86/x86_emulate/x86_emulate.c |  1 +
> xen/arch/x86/x86_emulate/x86_emulate.h | 32 ++++++++++++++++++++++----------
> 5 files changed, 48 insertions(+), 31 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
> index f1f6e2f..3efeead 100644
> --- a/xen/arch/x86/hvm/emulate.c
> +++ b/xen/arch/x86/hvm/emulate.c
> @@ -1770,13 +1770,6 @@ static int _hvm_emulate_one(struct hvm_emulate_ctxt 
> *hvmemul_ctxt,
> 
>     vio->mmio_retry = 0;
> 
> -    if ( cpu_has_vmx )
> -        hvmemul_ctxt->ctxt.swint_emulate = x86_swint_emulate_none;
> -    else if ( cpu_has_svm_nrips )
> -        hvmemul_ctxt->ctxt.swint_emulate = x86_swint_emulate_icebp;
> -    else
> -        hvmemul_ctxt->ctxt.swint_emulate = x86_swint_emulate_all;
> -
>     rc = x86_emulate(&hvmemul_ctxt->ctxt, ops);
> 
>     if ( rc == X86EMUL_OKAY && vio->mmio_retry )
> @@ -1947,14 +1940,23 @@ void hvm_emulate_init_once(
>     struct hvm_emulate_ctxt *hvmemul_ctxt,
>     struct cpu_user_regs *regs)
> {
> -    hvmemul_ctxt->intr_shadow = hvm_funcs.get_interrupt_shadow(current);
> -    hvmemul_ctxt->ctxt.regs = regs;
> -    hvmemul_ctxt->ctxt.force_writeback = 1;
> -    hvmemul_ctxt->seg_reg_accessed = 0;
> -    hvmemul_ctxt->seg_reg_dirty = 0;
> -    hvmemul_ctxt->set_context = 0;
> +    struct vcpu *curr = current;
> +
> +    memset(hvmemul_ctxt, 0, sizeof(*hvmemul_ctxt));
> +
> +    hvmemul_ctxt->intr_shadow = hvm_funcs.get_interrupt_shadow(curr);
>     hvmemul_get_seg_reg(x86_seg_cs, hvmemul_ctxt);
>     hvmemul_get_seg_reg(x86_seg_ss, hvmemul_ctxt);
> +
> +    hvmemul_ctxt->ctxt.regs = regs;
> +    hvmemul_ctxt->ctxt.force_writeback = true;
> +
> +    if ( cpu_has_vmx )
> +        hvmemul_ctxt->ctxt.swint_emulate = x86_swint_emulate_none;
> +    else if ( cpu_has_svm_nrips )
> +        hvmemul_ctxt->ctxt.swint_emulate = x86_swint_emulate_icebp;
> +    else
> +        hvmemul_ctxt->ctxt.swint_emulate = x86_swint_emulate_all;
> }
> 
> void hvm_emulate_init_per_insn(
> diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
> index 5b0e9f3..d365f59 100644
> --- a/xen/arch/x86/mm.c
> +++ b/xen/arch/x86/mm.c
> @@ -5337,7 +5337,14 @@ int ptwr_do_page_fault(struct vcpu *v, unsigned long 
> addr,
>     struct domain *d = v->domain;
>     struct page_info *page;
>     l1_pgentry_t      pte;
> -    struct ptwr_emulate_ctxt ptwr_ctxt;
> +    struct ptwr_emulate_ctxt ptwr_ctxt = {
> +        .ctxt = {
> +            .regs = regs,
> +            .addr_size = is_pv_32bit_domain(d) ? 32 : BITS_PER_LONG,
> +            .sp_size   = is_pv_32bit_domain(d) ? 32 : BITS_PER_LONG,
> +            .swint_emulate = x86_swint_emulate_none,
> +        },
> +    };
>     int rc;
> 
>     /* Attempt to read the PTE that maps the VA being accessed. */
> @@ -5363,11 +5370,6 @@ int ptwr_do_page_fault(struct vcpu *v, unsigned long 
> addr,
>         goto bail;
>     }
> 
> -    ptwr_ctxt.ctxt.regs = regs;
> -    ptwr_ctxt.ctxt.force_writeback = 0;
> -    ptwr_ctxt.ctxt.addr_size = ptwr_ctxt.ctxt.sp_size =
> -        is_pv_32bit_domain(d) ? 32 : BITS_PER_LONG;
> -    ptwr_ctxt.ctxt.swint_emulate = x86_swint_emulate_none;
>     ptwr_ctxt.cr2 = addr;
>     ptwr_ctxt.pte = pte;
> 
> diff --git a/xen/arch/x86/mm/shadow/common.c b/xen/arch/x86/mm/shadow/common.c
> index 7e5b8b0..a4a3c4b 100644
> --- a/xen/arch/x86/mm/shadow/common.c
> +++ b/xen/arch/x86/mm/shadow/common.c
> @@ -385,8 +385,9 @@ const struct x86_emulate_ops *shadow_init_emulation(
>     struct vcpu *v = current;
>     unsigned long addr;
> 
> +    memset(sh_ctxt, 0, sizeof(*sh_ctxt));
> +
>     sh_ctxt->ctxt.regs = regs;
> -    sh_ctxt->ctxt.force_writeback = 0;
>     sh_ctxt->ctxt.swint_emulate = x86_swint_emulate_none;
> 
>     if ( is_pv_vcpu(v) )
> @@ -396,7 +397,6 @@ const struct x86_emulate_ops *shadow_init_emulation(
>     }
> 
>     /* Segment cache initialisation. Primed with CS. */
> -    sh_ctxt->valid_seg_regs = 0;
>     creg = hvm_get_seg_reg(x86_seg_cs, sh_ctxt);
> 
>     /* Work out the emulation mode. */
> diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c 
> b/xen/arch/x86/x86_emulate/x86_emulate.c
> index d82e85d..532bd32 100644
> --- a/xen/arch/x86/x86_emulate/x86_emulate.c
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.c
> @@ -1904,6 +1904,7 @@ x86_decode(
>     state->regs = ctxt->regs;
>     state->eip = ctxt->regs->eip;
> 
> +    /* Initialise output state in x86_emulate_ctxt */
>     ctxt->retire.byte = 0;
> 
>     op_bytes = def_op_bytes = ad_bytes = def_ad_bytes = ctxt->addr_size/8;
> diff --git a/xen/arch/x86/x86_emulate/x86_emulate.h 
> b/xen/arch/x86/x86_emulate/x86_emulate.h
> index ec824ce..ab566c0 100644
> --- a/xen/arch/x86/x86_emulate/x86_emulate.h
> +++ b/xen/arch/x86/x86_emulate/x86_emulate.h
> @@ -410,6 +410,23 @@ struct cpu_user_regs;
> 
> struct x86_emulate_ctxt
> {
> +    /*
> +     * Input-only state:
> +     */
> +
> +    /* Software event injection support. */
> +    enum x86_swint_emulation swint_emulate;
> +
> +    /* Set this if writes may have side effects. */
> +    bool force_writeback;
> +
> +    /* Caller data that can be used by x86_emulate_ops' routines. */
> +    void *data;
> +
> +    /*
> +     * Input/output state:
> +     */
> +
>     /* Register state before/after emulation. */
>     struct cpu_user_regs *regs;
> 
> @@ -419,14 +436,12 @@ struct x86_emulate_ctxt
>     /* Stack pointer width in bits (16, 32 or 64). */
>     unsigned int sp_size;
> 
> -    /* Canonical opcode (see below). */
> -    unsigned int opcode;
> -
> -    /* Software event injection support. */
> -    enum x86_swint_emulation swint_emulate;
> +    /*
> +     * Output-only state:
> +     */
> 
> -    /* Set this if writes may have side effects. */
> -    uint8_t force_writeback;
> +    /* Canonical opcode (see below) (valid only on X86EMUL_OKAY). */
> +    unsigned int opcode;
> 
>     /* Retirement state, set by the emulator (valid only on X86EMUL_OKAY). */
>     union {
> @@ -437,9 +452,6 @@ struct x86_emulate_ctxt
>         } flags;
>         uint8_t byte;
>     } retire;
> -
> -    /* Caller data that can be used by x86_emulate_ops' routines. */
> -    void *data;
> };
> 
> /*
> -- 
> 2.1.4
> 


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