| Message ID | 20200901105445.22277-3-roger.pau@citrix.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | x86: switch default MSR behavior | expand |
On 01.09.2020 12:54, Roger Pau Monne wrote: > The SYSCFG, TOP_MEM1 and TOP_MEM2 MSRs are currently exposed to guests > and writes are silently discarded. Make this explicit in the SVM code > now, and just return default constant values when attempting to read > any of the MSRs, while continuing to silently drop writes. > > Signed-off-by: Roger Pau Monné <roger.pau@citrix.com> Reviewed-by: Jan Beulich <jbeulich@suse.com> > --- a/xen/arch/x86/hvm/svm/svm.c > +++ b/xen/arch/x86/hvm/svm/svm.c > @@ -1917,6 +1917,9 @@ static int svm_msr_read_intercept(unsigned int msr, uint64_t *msr_content) > goto gpf; > break; > > + case MSR_K8_SYSCFG: > + case MSR_K8_TOP_MEM1: > + case MSR_K8_TOP_MEM2: > case MSR_K8_VM_CR: > *msr_content = 0; > break; Andrew, since you did suggest otherwise before, may I ask for an explicit statement of yours here, be it in ack/nak form or something less formal? Jan
On 04/09/2020 09:36, Jan Beulich wrote: > On 01.09.2020 12:54, Roger Pau Monne wrote: >> The SYSCFG, TOP_MEM1 and TOP_MEM2 MSRs are currently exposed to guests >> and writes are silently discarded. Make this explicit in the SVM code >> now, and just return default constant values when attempting to read >> any of the MSRs, while continuing to silently drop writes. >> >> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com> > Reviewed-by: Jan Beulich <jbeulich@suse.com> > >> --- a/xen/arch/x86/hvm/svm/svm.c >> +++ b/xen/arch/x86/hvm/svm/svm.c >> @@ -1917,6 +1917,9 @@ static int svm_msr_read_intercept(unsigned int msr, uint64_t *msr_content) >> goto gpf; >> break; >> >> + case MSR_K8_SYSCFG: >> + case MSR_K8_TOP_MEM1: >> + case MSR_K8_TOP_MEM2: >> case MSR_K8_VM_CR: >> *msr_content = 0; >> break; > Andrew, since you did suggest otherwise before, may I ask for an > explicit statement of yours here, be it in ack/nak form or something > less formal? I'm not entirely convinced it is a safe thing to do, but lets see what happens. There is likely to be a bug tail from the flipping the default behaviour at the end of the series, and this is certainly a simpler set of logic than the alternative. ~Andrew
diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c index ca3bbfcbb3..af584ff5d1 100644 --- a/xen/arch/x86/hvm/svm/svm.c +++ b/xen/arch/x86/hvm/svm/svm.c @@ -1917,6 +1917,9 @@ static int svm_msr_read_intercept(unsigned int msr, uint64_t *msr_content) goto gpf; break; + case MSR_K8_SYSCFG: + case MSR_K8_TOP_MEM1: + case MSR_K8_TOP_MEM2: case MSR_K8_VM_CR: *msr_content = 0; break; @@ -2094,6 +2097,9 @@ static int svm_msr_write_intercept(unsigned int msr, uint64_t msr_content) goto gpf; break; + case MSR_K8_TOP_MEM1: + case MSR_K8_TOP_MEM2: + case MSR_K8_SYSCFG: case MSR_K8_VM_CR: /* ignore write. handle all bits as read-only. */ break;
The SYSCFG, TOP_MEM1 and TOP_MEM2 MSRs are currently exposed to guests and writes are silently discarded. Make this explicit in the SVM code now, and just return default constant values when attempting to read any of the MSRs, while continuing to silently drop writes. Signed-off-by: Roger Pau Monné <roger.pau@citrix.com> --- Changes since v2: - Return 0 from SYSCFG. - Merge switch cases. Changes sincxe v1: - Return MtrrFixDramEn in MSR_K8_SYSCFG. --- xen/arch/x86/hvm/svm/svm.c | 6 ++++++ 1 file changed, 6 insertions(+)