| Message ID | 20200820150835.27440-5-roger.pau@citrix.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | x86: switch default MSR behavior | expand |
On 20.08.2020 17:08, Roger Pau Monne wrote: > --- a/xen/arch/x86/hvm/svm/svm.c > +++ b/xen/arch/x86/hvm/svm/svm.c > @@ -2125,6 +2125,12 @@ static int svm_msr_write_intercept(unsigned int msr, uint64_t msr_content) > nsvm->ns_msr_hsavepa = msr_content; > break; > > + case MSR_F10_BU_CFG: > + /* See comment in svm_msr_read_intercept. */ > + if ( boot_cpu_data.x86 != 0xf ) > + goto gpf; > + break; This isn't how I understand the code and comment there: The dropping of writes applies to all families (and this being a Fam10 MSR, in particular Fam10). What the code there does is cover for the #GP that Xen received because the %rdi key wasn't correct. There wouldn't have been a #GP on Fam10. Newer families (didn't check yet where the boundary is) don't support this MSR anymore as per the BKDG (looking at Fam15's only right now). This may nevertheless still mean the CPUs return zero on reads and discard writes; we would want to mimic that behavior if so. And then, whatever the final behavior here, I guess we'd want to mirror it to the behavior for BU_CFG2, except perhaps for the Fam0F special case. Jan
diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c index 2d0823e7e1..7586b77268 100644 --- a/xen/arch/x86/hvm/svm/svm.c +++ b/xen/arch/x86/hvm/svm/svm.c @@ -2125,6 +2125,12 @@ static int svm_msr_write_intercept(unsigned int msr, uint64_t msr_content) nsvm->ns_msr_hsavepa = msr_content; break; + case MSR_F10_BU_CFG: + /* See comment in svm_msr_read_intercept. */ + if ( boot_cpu_data.x86 != 0xf ) + goto gpf; + break; + case MSR_AMD64_TSC_RATIO: if ( msr_content & TSC_RATIO_RSVD_BITS ) goto gpf;
We already have special casing to handle reads of this MSR for revF chips, so do as the comment in svm_msr_read_intercept says and drop writes. This is in preparation for changing the default MSR write behavior, which will instead return #GP on not explicitly handled writes. Signed-off-by: Roger Pau Monné <roger.pau@citrix.com> --- Changes since v1: - New in this version. --- xen/arch/x86/hvm/svm/svm.c | 6 ++++++ 1 file changed, 6 insertions(+)