Roman Kagan <rkagan@xxxxxxxxxxxxx> writes: > On Mon, Dec 10, 2018 at 01:54:18PM +0100, Vitaly Kuznetsov wrote: >> Roman Kagan <rkagan@xxxxxxxxxxxxx> writes: >> > Just noticed that the patch seems to assume that "direct" timers are >> > allowed to use any vectors including 0-15. I guess this is incorrect, >> > and instead stimer_set_config should error out on direct mode with a >> > vector less than HV_SYNIC_FIRST_VALID_VECTOR. >> >> The spec is really vague about this and I'm not sure that this has >> anything to do with HV_SYNIC_FIRST_VALID_VECTOR (as these are actually >> not "synic" vectors, I *think* that SynIC doesn't even need to be >> enabled to make them work). >> >> I checked and Hyper-V 2016 uses vector '0xff', not sure if it proves >> your point :-) >> >> Do you envision any issues in KVM if we keep allowing vectors < >> HV_SYNIC_FIRST_VALID_VECTOR? > > It's actually lapic that treats vectors 0..15 as illegal. Nothing > Hyper-V specific here. Oh, right you are, Intel SDM 10.5.2 "Valid Interrupt Vectors" says: "The Intel 64 and IA-32 architectures define 256 vector numbers, ranging from 0 through 255 (see Section 6.2, “Exception and Interrupt Vectors”). Local and I/O APICs support 240 of these vectors (in the range of 16 to 255) as valid interrupts. When an interrupt vector in the range of 0 to 15 is sent or received through the local APIC, the APIC indicates an illegal vector in its Error Status Register (see Section 10.5.3, “Error Handling”). The Intel 64 and IA-32 architectures reserve vectors 16 through 31 for predefined interrupts, exceptions, and Intel-reserved encodings (see Table 6-1). However, the local APIC does not treat vectors in this range as illegal." Out of pure curiosity I checked what Hyper-V does by hacking up linux and I got "unchecked MSR access error: WRMSR to 0x400000b0" so we know they follow the spec. I'll send a patch to fix this, thanks! -- Vitaly
