Re: [Xen-devel] [PATCH] x86/msr: Handle MSR_AMD64_DR{0-3}_ADDRESS_MASK in the new MSR infrastructure

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.11.18 at 14:41, <andrew.cooper3@xxxxxxxxxx> wrote:
> This is a followup to c/s 96f235c26 which fulfils the remaining TODO item.
> 
> First of all, the pre-existing SVM code has a bug.  The value in
> msrs->dr_mask[] may be stale, as we allow direct access to these MSRs.
> Resolve this in guest_rdmsr() by reading directly from hardware in the
> affected case.
> 
> With the reading/writing logic moved to the common guest_{rd,wr}msr()
> infrastructure, the migration logic can be simplified.  The PV migration logic
> drops all of its special casing, and SVM's entire {init,save,load}_msr()
> infrastructure becomes unnecessary.
> 
> The resulting diffstat shows quite how expensive the PV special cases where in
> arch_do_domctl().
> 
>   add/remove: 0/3 grow/shrink: 4/6 up/down: 465/-1494 (-1029)
>   Function                                     old     new   delta
>   guest_rdmsr                                  252     484    +232
>   guest_wrmsr                                  653     822    +169
>   msrs_to_send                                   8      48     +40
>   hvm_load_cpu_msrs                            489     513     +24
>   svm_init_msr                                  21       -     -21
>   hvm_save_cpu_msrs                            365     343     -22
>   read_msr                                    1089    1001     -88
>   write_msr                                   1829    1689    -140
>   svm_msr_read_intercept                      1124     970    -154
>   svm_load_msr                                 195       -    -195
>   svm_save_msr                                 196       -    -196
>   svm_msr_write_intercept                     1461    1265    -196
>   arch_do_domctl                              9581    9099    -482
>   Total: Before=3314610, After=3313581, chg -0.03%
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>



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