Re: [Xen-devel] [PATCH 8/9] x86/vmx: Support removing MSRs from the host/guest load/save lists

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 24/05/18 16:42, Roger Pau Monné wrote:
> On Tue, May 22, 2018 at 12:20:45PM +0100, Andrew Cooper wrote:
>> Up until this point, the MSR load/save lists have only ever accumulated
>> content.  Introduce vmx_del_msr() as a companion to vmx_add_msr().
>>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> ---
>> CC: Jan Beulich <JBeulich@xxxxxxxx>
>> CC: Jun Nakajima <jun.nakajima@xxxxxxxxx>
>> CC: Kevin Tian <kevin.tian@xxxxxxxxx>
>> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
>> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
>> ---
>>  xen/arch/x86/hvm/vmx/vmcs.c        | 68 
>> ++++++++++++++++++++++++++++++++++++++
>>  xen/include/asm-x86/hvm/vmx/vmcs.h |  1 +
>>  2 files changed, 69 insertions(+)
>>
>> diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
>> index 7bf19a0..e1a8f95 100644
>> --- a/xen/arch/x86/hvm/vmx/vmcs.c
>> +++ b/xen/arch/x86/hvm/vmx/vmcs.c
>> @@ -1465,6 +1465,74 @@ int vmx_add_msr(struct vcpu *v, uint32_t msr, 
>> uint64_t val,
>>      return rc;
>>  }
>>  
>> +int vmx_del_msr(struct vcpu *v, uint32_t msr, enum vmx_msr_list_type type)
>> +{
>> +    struct arch_vmx_struct *arch_vmx = &v->arch.hvm_vmx;
>> +    struct vmx_msr_entry *start = NULL, *ent, *end;
>> +    unsigned int substart, subend, total;
>> +
>> +    ASSERT(v == current || !vcpu_runnable(v));
>> +
>> +    switch ( type )
>> +    {
>> +    case VMX_MSR_HOST:
>> +        start    = arch_vmx->host_msr_area;
>> +        substart = 0;
>> +        subend   = arch_vmx->host_msr_count;
>> +        total    = subend;
>> +        break;
>> +
>> +    case VMX_MSR_GUEST:
>> +        start    = arch_vmx->msr_area;
>> +        substart = 0;
>> +        subend   = arch_vmx->msr_save_count;
>> +        total    = arch_vmx->msr_load_count;
>> +        break;
>> +
>> +    case VMX_MSR_GUEST_LOADONLY:
>> +        start    = arch_vmx->msr_area;
>> +        substart = arch_vmx->msr_save_count;
>> +        subend   = arch_vmx->msr_load_count;
>> +        total    = subend;
>> +        break;
>> +
>> +    default:
>> +        ASSERT_UNREACHABLE();
>> +    }
> The above chunk is already in vmx_find_msr and vmx_add_msr, maybe a
> static helper that sets start/substart/subend/total would be helpful
> here?

Its actually more than that.  They are identical identical until after
the locate_msr_entry() call.  The problem is that I can't find a clean
way of collecting the logic which is also readable.

I'd also like to fold together the add side, but that is further
complicated by the memory allocation logic.

~Andrew

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