Messages in this thread | | | Date | Fri, 31 Mar 2023 17:09:16 +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 08:40:30AM -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?
-- Kiryl Shutsemau / Kirill A. Shutemov
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