Re: [Xen-devel] [PATCH] x86/svm: Fix svm_vmcb_dump() when used in current context

["Woods, Brian" <Brian.Woods@xxxxxxx>]

On Mon, Jun 17, 2019 at 01:54:39PM +0100, Andy Cooper wrote:
> VMExit doesn't switch all state.  The FS/GS/TS/LDTR/GSBASE segment
> information, and SYSCALL/SYSENTER MSRs may still be cached in hardware, rather
> than up-to-date in the VMCB.
> 
> Export svm_sync_vmcb() via svmdebug.h so svm_vmcb_dump() can use it, and bring
> the VMCB into sync in current context.
> 
> As a minor optimisation, switch svm_sync_vmcb() to use svm_vm{load,save}_pa(),
> as svm->vmcb_pa is always in correct, and this avoids a redundant __pa()
> translation behind the scenes.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Acked-by: Brian Woods <brian.woods@xxxxxxx>

> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Wei Liu <wl@xxxxxxx>
> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> CC: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> CC: Brian Woods <brian.woods@xxxxxxx>
> ---
>  xen/arch/x86/hvm/svm/svm.c             | 6 +++---
>  xen/arch/x86/hvm/svm/svmdebug.c        | 9 +++++++++
>  xen/include/asm-x86/hvm/svm/svmdebug.h | 1 +
>  3 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
> index cd6a6b3..0eac9ce 100644
> --- a/xen/arch/x86/hvm/svm/svm.c
> +++ b/xen/arch/x86/hvm/svm/svm.c
> @@ -627,21 +627,21 @@ static void svm_cpuid_policy_changed(struct vcpu *v)
>                        cp->extd.ibpb ? MSR_INTERCEPT_NONE : MSR_INTERCEPT_RW);
>  }
>  
> -static void svm_sync_vmcb(struct vcpu *v, enum vmcb_sync_state new_state)
> +void svm_sync_vmcb(struct vcpu *v, enum vmcb_sync_state new_state)
>  {
>      struct svm_vcpu *svm = &v->arch.hvm.svm;
>  
>      if ( new_state == vmcb_needs_vmsave )
>      {
>          if ( svm->vmcb_sync_state == vmcb_needs_vmload )
> -            svm_vmload(svm->vmcb);
> +            svm_vmload_pa(svm->vmcb_pa);
>  
>          svm->vmcb_sync_state = new_state;
>      }
>      else
>      {
>          if ( svm->vmcb_sync_state == vmcb_needs_vmsave )
> -            svm_vmsave(svm->vmcb);
> +            svm_vmsave_pa(svm->vmcb_pa);
>  
>          if ( svm->vmcb_sync_state != vmcb_needs_vmload )
>              svm->vmcb_sync_state = new_state;
> diff --git a/xen/arch/x86/hvm/svm/svmdebug.c b/xen/arch/x86/hvm/svm/svmdebug.c
> index d35e405..4293d8d 100644
> --- a/xen/arch/x86/hvm/svm/svmdebug.c
> +++ b/xen/arch/x86/hvm/svm/svmdebug.c
> @@ -29,6 +29,15 @@ static void svm_dump_sel(const char *name, const struct 
> segment_register *s)
>  
>  void svm_vmcb_dump(const char *from, const struct vmcb_struct *vmcb)
>  {
> +    struct vcpu *curr = current;
> +
> +    /*
> +     * If we are dumping the VMCB currently in context, some guest state may
> +     * still be cached in hardware.  Retrieve it.
> +     */
> +    if ( vmcb == curr->arch.hvm.svm.vmcb )
> +        svm_sync_vmcb(curr, vmcb_in_sync);
> +
>      printk("Dumping guest's current state at %s...\n", from);
>      printk("Size of VMCB = %zu, paddr = %"PRIpaddr", vaddr = %p\n",
>             sizeof(struct vmcb_struct), virt_to_maddr(vmcb), vmcb);
> diff --git a/xen/include/asm-x86/hvm/svm/svmdebug.h 
> b/xen/include/asm-x86/hvm/svm/svmdebug.h
> index 658cdd3..330c1d9 100644
> --- a/xen/include/asm-x86/hvm/svm/svmdebug.h
> +++ b/xen/include/asm-x86/hvm/svm/svmdebug.h
> @@ -22,6 +22,7 @@
>  #include <asm/types.h>
>  #include <asm/hvm/svm/vmcb.h>
>  
> +void svm_sync_vmcb(struct vcpu *v, enum vmcb_sync_state new_state);
>  void svm_vmcb_dump(const char *from, const struct vmcb_struct *vmcb);
>  bool svm_vmcb_isvalid(const char *from, const struct vmcb_struct *vmcb,
>                        const struct vcpu *v, bool verbose);
> -- 
> 2.1.4
> 

-- 
Brian Woods

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