Messages in this thread | | | Date | Mon, 05 Jul 2010 10:54:20 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH v2] KVM: IOAPIC: only access APIC registers one dword at a time |
| |
On 07/05/2010 06:47 AM, Xiao Guangrong wrote: > > Avi Kivity wrote: > >> On 07/02/2010 11:00 AM, Xiao Guangrong wrote: >> >>> The IOAPIC spec says: >>> >>> When accessing these registers, accesses must be done one dword at a >>> time. >>> For example, software should never access byte 2 from the Data >>> register before >>> accessing bytes 0 and 1. The hardware will not attempt to recover from >>> a bad >>> programming model in this case. >>> >>> So, this patch removes other width access >>> >>> >>> >> The ioapic code also implements the ia64 iosapic. I'm guessing that >> does support 64-bit accesses. Please check the iosapic documentation. >> >> > The iosapic also using 32-bit to access registers: > > All registers are accessed using 32-bit uncacheable loads and stores to a reserved memory location > in system memory. This implies that to modify a field (e.g., a bit or a byte) in any register, the > whole 32-bit register must be read, the field modified, and the 32 bits written back. Partial register > access, or non-aligned register access, are implementation-defined by the I/O xAPIC and will not > be compatible across different implementations. Also, registers that are described as 64 bits wide > are accessed as multiple independent 32-bit registers. > > [ From<< Intel® Itanium® Processor Family Interrupt Architecture Guide>>, P2-6 ] >
Ok.
>> There might be guests that use incorrect access despite the >> documentation; if real hardware supports it, it should work. So we need >> to start with just a warning, and allow the access. Later we can drop >> the invalid access. >> > If the OS contravene the spec, i thinks it's the OS's bug, also, i have tested some versions > windows/linux guests, it's no broken, can we directly drop the other wide access? >
Well, there's the spec and there's real life, but in this case we can try and if we see a problem we'll re-add the other access length.
-- error compiling committee.c: too many arguments to function
-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |