Messages in this thread | | | Date | Fri, 31 Mar 2023 09:33:31 -0500 | Subject | Re: [RFC PATCH] x86/insn: support decode MOVSXD instruction for MMIO | From | Tom Lendacky <> |
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On 3/31/23 09:09, Kirill A. Shutemov wrote: > On Fri, Mar 31, 2023 at 08:40:30AM -0500, Tom Lendacky wrote: >> On 3/31/23 05:06, Kirill A. Shutemov wrote: >>> On Fri, Mar 31, 2023 at 08:49:48AM +0000, David Laight wrote: >>>> From: Wu Zongyong >>>>> Sent: 31 March 2023 03:24 >>>>> >>>>> On Thu, Mar 30, 2023 at 03:39:51PM +0300, kirill.shutemov@linux.intel.com wrote: >>>>>> On Wed, Mar 29, 2023 at 10:59:37AM +0800, Wu Zongyong wrote: >>>>>>> It seems MOVSXD which opcode is 0x63 is not handled, support >>>>>>> to decode it in insn_decode_mmio(). >>>>>> >>>>>> Do you have a particular user in mind? >>>>> To be honest, I don't find a specific user which uses the MOVSXD. >>>>> >>>>> But both Intel and AMD's instructions reference contains MOVSXD and lots >>>>> of MOVSXD instructions occur when I "objdump -S vmlinux", so I think it >>>>> may be useful to support it in insn_decode_mmio(). >>>>> >>>>> Are there some special consideration about this instruction? >>>> >>>> It is a sign-extending memory read (32bit to 64bit). >>>> You pretty much never want to do that to a device register. >>>> Also kernel code should be using readl() (etc) which do >>>> unsigned reads. >>>> So they should never happen for mmio. >>>> >>>> Of course, if you mmap() PCIe space directly into a program's >>>> address space anything might happen ... >>> >>> There are two users of the interface: TDX and SEV. TDX doesn't allow >>> userspace MMIO. SEV *seems* allows it, but I am not sure how it is safe. >>> >>> Tom? >> >> The insn_decode_mmio() function is only called by the SEV/TDX related code >> and is specifically MMIO oriented. As David said, this instruction is likely >> not being used for that in the kernel. If we come across a case where this >> is used, we can look at how it is being used in that situation and it can be >> addressed then. > > I was asking if SEV supports userspace MMIO. And if yes, how do you make > it safe? >
No, SEV doesn't support userspace MMIO.
Thanks, Tom
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