[Qemu-devel] [Bug 1809144] [NEW] SVM instructions fail with SVME bit enabled

[Qemu-devel] [Bug 1809144] [NEW] SVM instructions fail with SVME bit enabled

[Paolo Montesel]

Public bug reported:

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
vmsave
```

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);
                break;
            }
```

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.

Cheers,

thebabush

** Affects: qemu
     Importance: Undecided
         Status: New

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Title:
  SVM instructions fail with SVME bit enabled

Status in QEMU:
  New

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
  vmsave
  ```

  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);
                  break;
              }
  ```

  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.

  Cheers,

  thebabush

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Re: [Qemu-devel] [Bug 1809144] [NEW] SVM instructions fail with SVME bit enabled

[Richard Henderson]

On 12/19/18 9:31 AM, Paolo Montesel wrote:
> A quick fix is to make the tb end after `wrmsr` instructions, but it's an hack afaik.

No, that's exactly the correct solution.


r~

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

[Thomas Huth]

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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https://bugs.launchpad.net/bugs/1809144

Title:
  SVM instructions fail with SVME bit enabled

Status in QEMU:
  Incomplete

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
  vmsave
  ```

  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);
                  break;
              }
  ```

  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.

  Cheers,

  thebabush

To manage notifications about this bug go to:
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[Bug 1809144] Re: SVM instructions fail with SVME bit enabled

[Launchpad Bug Tracker]

[Expired for QEMU because there has been no activity for 60 days.]

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

-- 
You received this bug notification because you are a member of qemu-
devel-ml, which is subscribed to QEMU.
https://bugs.launchpad.net/bugs/1809144

Title:
  SVM instructions fail with SVME bit enabled

Status in QEMU:
  Expired

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
  vmsave
  ```

  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);
                  break;
              }
  ```

  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.

  Cheers,

  thebabush

To manage notifications about this bug go to:
https://bugs.launchpad.net/qemu/+bug/1809144/+subscriptions