Messages in this thread | | | Date | Fri, 31 Mar 2023 13:06:20 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [RFC PATCH] x86/insn: support decode MOVSXD instruction for MMIO |
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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?
-- Kiryl Shutsemau / Kirill A. Shutemov
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