[kvm-unit-tests PATCH 0/2] x86: Fixes for rdpid test

[kvm-unit-tests PATCH 0/2] x86: Fixes for rdpid test

[David Matlack]

Fix 2 small issues with the rdpid test that is a part of x86/tsc.c.
Notably, the test is not currently running since qemu is not configured
to advertise RDPID support and fixing that uncovers a bug in the test
when compiling with Clang.

David Matlack (2):
  x86: Run the tsc test with -cpu max
  x86: Mark RDPID asm volatile to avoid dropping instructions

 x86/tsc.c         | 2 +-
 x86/unittests.cfg | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)


base-commit: e3c5c3ef2524c58023073c0fadde2e8ae3c04ec6
-- 
2.40.0.rc0.216.gc4246ad0f0-goog

[kvm-unit-tests PATCH 1/2] x86: Run the tsc test with -cpu max

[David Matlack]

Run the tsc test with -cpu max to enable RDPID testing. The current
configuration (-cpu kvm64,+rdtscp) does not include RDPID even if the
host supports. In effect, test_rdpid() never runs.

Use max instead of adding +rdpid to the existing configuration to avoid
this biting someone in the future if they add a test for a new feature.

Fixes: 10631a5bebd8 ("x86: tsc: add rdpid test")
Signed-off-by: David Matlack <dmatlack@google.com>
---
 x86/unittests.cfg | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/x86/unittests.cfg b/x86/unittests.cfg
index f324e32d60ef..c4eaa8ef9bab 100644
--- a/x86/unittests.cfg
+++ b/x86/unittests.cfg
@@ -247,7 +247,7 @@ extra_params = -cpu Opteron_G1,vendor=AuthenticAMD
 
 [tsc]
 file = tsc.flat
-extra_params = -cpu kvm64,+rdtscp
+extra_params = -cpu max
 
 [tsc_adjust]
 file = tsc_adjust.flat
-- 
2.40.0.rc0.216.gc4246ad0f0-goog

[kvm-unit-tests PATCH 2/2] x86: Mark RDPID asm volatile to avoid dropping instructions

[David Matlack]

Mark the asm statement that generates the RDPID instruction volatile.
The compiler within its rights to drop subsequent RDPID asm statements
(after the first) since the inputs never change.

This fixes the tsc test on hardware that supports rdpid when built with
the latest Clang compiler.

Fixes: 10631a5bebd8 ("x86: tsc: add rdpid test")
Reported-by: Greg Thelen <gthelen@google.com>
Suggested-by: Greg Thelen <gthelen@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
---
 x86/tsc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/x86/tsc.c b/x86/tsc.c
index bc403fc78461..b3bb120291ec 100644
--- a/x86/tsc.c
+++ b/x86/tsc.c
@@ -24,7 +24,7 @@ static void test_rdpid(u64 aux)
        u32 eax;
 
        wrmsr(MSR_TSC_AUX, aux);
-       asm (".byte 0xf3, 0x0f, 0xc7, 0xf8" : "=a" (eax));
+       asm volatile (".byte 0xf3, 0x0f, 0xc7, 0xf8" : "=a" (eax));
        report(eax == aux, "Test rdpid %%eax %" PRId64, aux);
 }
 
-- 
2.40.0.rc0.216.gc4246ad0f0-goog

Re: [kvm-unit-tests PATCH 2/2] x86: Mark RDPID asm volatile to avoid dropping instructions

[Jim Mattson]

On Mon, Mar 6, 2023 at 4:56 PM David Matlack <dmatlack@google.com> wrote:
>
> Mark the asm statement that generates the RDPID instruction volatile.
> The compiler within its rights to drop subsequent RDPID asm statements
> (after the first) since the inputs never change.
>
> This fixes the tsc test on hardware that supports rdpid when built with
> the latest Clang compiler.
>
> Fixes: 10631a5bebd8 ("x86: tsc: add rdpid test")
> Reported-by: Greg Thelen <gthelen@google.com>
> Suggested-by: Greg Thelen <gthelen@google.com>
> Signed-off-by: David Matlack <dmatlack@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>

Re: [kvm-unit-tests PATCH 0/2] x86: Fixes for rdpid test

[Paolo Bonzini]

On 3/7/23 01:55, David Matlack wrote:
> Fix 2 small issues with the rdpid test that is a part of x86/tsc.c.
> Notably, the test is not currently running since qemu is not configured
> to advertise RDPID support and fixing that uncovers a bug in the test
> when compiling with Clang.
> 
> David Matlack (2):
>    x86: Run the tsc test with -cpu max
>    x86: Mark RDPID asm volatile to avoid dropping instructions
> 
>   x86/tsc.c         | 2 +-
>   x86/unittests.cfg | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
> 
> 
> base-commit: e3c5c3ef2524c58023073c0fadde2e8ae3c04ec6

Queued, thanks.

Paolo

Re: [kvm-unit-tests PATCH 0/2] x86: Fixes for rdpid test

[Sean Christopherson]

On Mon, 06 Mar 2023 16:55:45 -0800, David Matlack wrote:
> Fix 2 small issues with the rdpid test that is a part of x86/tsc.c.
> Notably, the test is not currently running since qemu is not configured
> to advertise RDPID support and fixing that uncovers a bug in the test
> when compiling with Clang.
> 
> David Matlack (2):
>   x86: Run the tsc test with -cpu max
>   x86: Mark RDPID asm volatile to avoid dropping instructions
> 
> [...]

Applied to kvm-x86 next, thanks!  Paolo's "Queued, thanks" showed up, but I
don't see these in upstream.

[1/2] x86: Run the tsc test with -cpu max
      https://github.com/kvm-x86/kvm-unit-tests/commit/572fb7097fa7
[2/2] x86: Mark RDPID asm volatile to avoid dropping instructions
      https://github.com/kvm-x86/kvm-unit-tests/commit/a467f7679c7f

--
https://github.com/kvm-x86/kvm-unit-tests/tree/next