Re: [PATCH v3 3/3] x86: Clean up the Xen MSR infrastructure

[Sergey Dyasli <sergey.dyasli@citrix.com>]

On Tue, 2018-09-11 at 19:56 +0100, Andrew Cooper wrote:
> Rename them to guest_{rd,wr}msr_xen() for consistency, and because the _regs
> suffix isn't very appropriate.
> 
> Update them to take a vcpu pointer rather than presuming that they act on
> current, and switch to using X86EMUL_* return values.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
> ---
> CC: Jan Beulich <JBeulich@suse.com>
> CC: Wei Liu <wei.liu2@citrix.com>
> CC: Roger Pau Monné <roger.pau@citrix.com>
> CC: Sergey Dyasli <sergey.dyasli@citrix.com>
> 
> v3:
>  * Clean up after splitting the series.
> ---
>  xen/arch/x86/msr.c              |  6 ++----
>  xen/arch/x86/traps.c            | 29 +++++++++++++----------------
>  xen/include/asm-x86/processor.h |  4 ++--
>  3 files changed, 17 insertions(+), 22 deletions(-)
> 
> diff --git a/xen/arch/x86/msr.c b/xen/arch/x86/msr.c
> index cf0dc27..8f02a89 100644
> --- a/xen/arch/x86/msr.c
> +++ b/xen/arch/x86/msr.c
> @@ -156,8 +156,7 @@ int guest_rdmsr(const struct vcpu *v, uint32_t msr, uint64_t *val)
>  
>          /* Fallthrough. */
>      case 0x40000200 ... 0x400002ff:
> -        ret = (rdmsr_hypervisor_regs(msr, val)
> -               ? X86EMUL_OKAY : X86EMUL_EXCEPTION);
> +        ret = guest_rdmsr_xen(v, msr, val);
>          break;
>  
>      default:
> @@ -277,8 +276,7 @@ int guest_wrmsr(struct vcpu *v, uint32_t msr, uint64_t val)
>  
>          /* Fallthrough. */
>      case 0x40000200 ... 0x400002ff:
> -        ret = (wrmsr_hypervisor_regs(msr, val) == 1
> -               ? X86EMUL_OKAY : X86EMUL_EXCEPTION);
> +        ret = guest_wrmsr_xen(v, msr, val);
>          break;
>  
>      default:
> diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
> index 7c17806..3988753 100644
> --- a/xen/arch/x86/traps.c
> +++ b/xen/arch/x86/traps.c
> @@ -768,29 +768,25 @@ static void do_trap(struct cpu_user_regs *regs)
>            trapnr, trapstr(trapnr), regs->error_code);
>  }
>  
> -/* Returns 0 if not handled, and non-0 for success. */
> -int rdmsr_hypervisor_regs(uint32_t idx, uint64_t *val)
> +int guest_rdmsr_xen(const struct vcpu *v, uint32_t idx, uint64_t *val)
>  {
> -    struct domain *d = current->domain;
> +    const struct domain *d = v->domain;
>      /* Optionally shift out of the way of Viridian architectural MSRs. */
>      uint32_t base = is_viridian_domain(d) ? 0x40000200 : 0x40000000;
>  
>      switch ( idx - base )
>      {
>      case 0: /* Write hypercall page MSR.  Read as zero. */
> -    {
>          *val = 0;
> -        return 1;
> -    }
> +        return X86EMUL_OKAY;
>      }
>  
> -    return 0;
> +    return X86EMUL_EXCEPTION;
>  }
>  
> -/* Returns 1 if handled, 0 if not and -Exx for error. */
> -int wrmsr_hypervisor_regs(uint32_t idx, uint64_t val)
> +int guest_wrmsr_xen(struct vcpu *v, uint32_t idx, uint64_t val)
>  {
> -    struct domain *d = current->domain;
> +    struct domain *d = v->domain;
>      /* Optionally shift out of the way of Viridian architectural MSRs. */
>      uint32_t base = is_viridian_domain(d) ? 0x40000200 : 0x40000000;
>  
> @@ -809,7 +805,7 @@ int wrmsr_hypervisor_regs(uint32_t idx, uint64_t val)
>              gdprintk(XENLOG_WARNING,
>                       "wrmsr hypercall page index %#x unsupported\n",
>                       page_index);
> -            return 0;
> +            return X86EMUL_EXCEPTION;
>          }
>  
>          page = get_page_from_gfn(d, gmfn, &t, P2M_ALLOC);
> @@ -822,13 +818,13 @@ int wrmsr_hypervisor_regs(uint32_t idx, uint64_t val)
>              if ( p2m_is_paging(t) )
>              {
>                  p2m_mem_paging_populate(d, gmfn);
> -                return -ERESTART;
> +                return X86EMUL_RETRY;

Previously -ERESTART would've been converted to X86EMUL_EXCEPTION. But
with this patch, X86EMUL_RETRY will actually be returned. I don't think
that callers can handle this situation.

E.g. the code from vmx_vmexit_handler():

    case EXIT_REASON_MSR_WRITE:
        switch ( hvm_msr_write_intercept(regs->ecx, msr_fold(regs), 1) )
        {
        case X86EMUL_OKAY:
            update_guest_eip(); /* Safe: WRMSR */
            break;

        case X86EMUL_EXCEPTION:
            hvm_inject_hw_exception(TRAP_gp_fault, 0);
            break;
        }
        break;

>              }
>  
>              gdprintk(XENLOG_WARNING,
>                       "Bad GMFN %lx (MFN %#"PRI_mfn") to MSR %08x\n",
>                       gmfn, mfn_x(page ? page_to_mfn(page) : INVALID_MFN), base);
> -            return 0;
> +            return X86EMUL_EXCEPTION;
>          }
>  
>          hypercall_page = __map_domain_page(page);
> @@ -836,11 +832,12 @@ int wrmsr_hypervisor_regs(uint32_t idx, uint64_t val)
>          unmap_domain_page(hypercall_page);
>  
>          put_page_and_type(page);
> -        return 1;
> -    }
> +        return X86EMUL_OKAY;
>      }
>  
> -    return 0;
> +    default:
> +        return X86EMUL_EXCEPTION;
> +    }
>  }
>  
>  void cpuid_hypervisor_leaves(const struct vcpu *v, uint32_t leaf,
> diff --git a/xen/include/asm-x86/processor.h b/xen/include/asm-x86/processor.h
> index a166802..03555e1 100644
> --- a/xen/include/asm-x86/processor.h
> +++ b/xen/include/asm-x86/processor.h
> @@ -554,8 +554,8 @@ unsigned long alloc_stub_page(unsigned int cpu, unsigned long *mfn);
>  
>  void cpuid_hypervisor_leaves(const struct vcpu *v, uint32_t leaf,
>                               uint32_t subleaf, struct cpuid_leaf *res);
> -int rdmsr_hypervisor_regs(uint32_t idx, uint64_t *val);
> -int wrmsr_hypervisor_regs(uint32_t idx, uint64_t val);
> +int guest_rdmsr_xen(const struct vcpu *v, uint32_t idx, uint64_t *val);
> +int guest_wrmsr_xen(struct vcpu *v, uint32_t idx, uint64_t val);
>  
>  void microcode_set_module(unsigned int);
>  int microcode_update(XEN_GUEST_HANDLE_PARAM(const_void), unsigned long len);
-- 
Thanks,
Sergey
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