On 20.10.20 11:27, Paolo Bonzini wrote:
On 19/10/20 19:45, Graf (AWS), Alexander wrote:
+ * In principle it would be possible to trap x2apic ranges
+ * if !lapic_in_kernel. This however would be complicated
+ * because KVM_X86_SET_MSR_FILTER can be called before
+ * KVM_CREATE_IRQCHIP or KVM_ENABLE_CAP.
+ */
+ for (i = 0; i < ARRAY_SIZE(filter.ranges); i++)
+ if (range_overlaps_x2apic(&filter.ranges[i]))
+ return -EINVAL;
What if the default action of the filter is to "deny"? Then only an
MSR filter to allow access to x2apic MSRs would make the full
filtering logic adhere to the constraints, no?
Right; or more precisely, that is handled by Sean's patch that he had
posted earlier. This patch only makes it impossible to set up such a
filter.
What I'm saying is that a "filter rule" can either mean "allow" or
"deny". Here you're only checking if there is a rule. What you want to
filter for is whether there is a denying rule (including default
fallback) for x2apic after all rules are in place.
Imagine you add the following filter:
{
count: 1,
default_allow: false,
ranges: [
{
flags: KVM_MSR_FILTER_READ,
nmsrs: 1,
base: MSR_EFER,
bitmap: { 1 },
},
],
}
That filter would set all x2apic registers to "deny", but would not be
caught by the code above. Conversely, a range that explicitly allows
x2apic ranges with default_allow=0 would be rejected by this patch.
Alex
Amazon Development Center Germany GmbH
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