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[Bug 1809144] Re: SVM instructions fail with SVME bit enabled

From: Thomas Huth
Subject: [Bug 1809144] Re: SVM instructions fail with SVME bit enabled
Date: Tue, 20 Apr 2021 07:57:08 -0000

The QEMU project is currently considering to move its bug tracking to another 
system. For this we need to know which bugs are still valid and which could be 
closed already. Thus we are setting older bugs to "Incomplete" now.
If you still think this bug report here is valid, then please switch the state 
back to "New" within the next 60 days, otherwise this report will be marked as 
"Expired". Or mark it as "Fix Released" if the problem has been solved with a 
newer version of QEMU already. Thank you and sorry for the inconvenience.

** Changed in: qemu
       Status: New => Incomplete

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  SVM instructions fail with SVME bit enabled

Status in QEMU:

Bug description:
  I was trying to use QEMU/TCG to emulate some stuff that uses SVM.
  I know SVM is only partially implemented but I gave it a try anyway.

  I found that if SVM is enabled in the same basic block in which there's a 
call to VMSAVE/etc,
  the call fails as illegal op because the flags don't get updated correctly.

  The pseudocode for the asm I'm running is:

  EFER |= SVME; set the appropriate bit with wrmsr

  This is an example of the relevant translate.c code:

              if (!(s->flags & HF_SVME_MASK) || !s->pe) {
                  goto illegal_op;
              if (s->cpl != 0) {
                  gen_exception(s, EXCP0D_GPF, pc_start - s->cs_base);

  s->flags doesn't get updated after the wrmsr instruction and so QEMU
  raises an illegal opcode interrupt.

  A quick fix is to make the tb end after `wrmsr` instructions, but it's an 
hack afaik.
  I'm not too comfortable with QEMU's code, so I don't know what a proper fix 
would be.



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