Hi Marc,
On 06/02/2024 12:17, Marc Zyngier wrote:
Hi Sumit,
On Tue, 06 Feb 2024 11:48:52 +0000,
Sumit Gupta <sumitg@xxxxxxxxxx> wrote:
MC SID register access is restricted for Guest VM.
So, skip the SID override programming from the Guest VM.
Signed-off-by: Sumit Gupta <sumitg@xxxxxxxxxx>
---
drivers/memory/tegra/tegra186.c | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/drivers/memory/tegra/tegra186.c b/drivers/memory/tegra/tegra186.c
index 1b3183951bfe..df441896b69d 100644
--- a/drivers/memory/tegra/tegra186.c
+++ b/drivers/memory/tegra/tegra186.c
@@ -10,6 +10,7 @@
#include <linux/of.h>
#include <linux/of_platform.h>
#include <linux/platform_device.h>
+#include <asm/virt.h>
#include <soc/tegra/mc.h>
@@ -118,6 +119,11 @@ static int tegra186_mc_probe_device(struct tegra_mc *mc, struct device *dev)
unsigned int i, index = 0;
u32 sid;
+ if (!is_kernel_in_hyp_mode()) {
+ dev_dbg(mc->dev, "Register access not allowed\n");
+ return 0;
+ }
+
if (!tegra_dev_iommu_get_stream_id(dev, &sid))
return 0;
@@ -146,6 +152,11 @@ static int tegra186_mc_resume(struct tegra_mc *mc)
#if IS_ENABLED(CONFIG_IOMMU_API)
unsigned int i;
+ if (!is_kernel_in_hyp_mode()) {
+ dev_dbg(mc->dev, "Register access not allowed\n");
+ return 0;
+ }
+
for (i = 0; i < mc->soc->num_clients; i++) {
const struct tegra_mc_client *client = &mc->soc->clients[i];
This doesn't look right. Multiple reasons:
- This helper really has nothing to do in a driver. This is
architectural stuff that is not intended for use outside of arch
core code.
We see a few other drivers using this ...
drivers/perf/arm_pmuv3.c
drivers/clocksource/arm_arch_timer.c
drivers/gpu/drm/amd/amdgpu/amdgpu_virt.h
drivers/hwtracing/coresight/coresight-etm4x-core.c
drivers/hwtracing/coresight/coresight-etm4x-core.c
drivers/irqchip/irq-apple-aic.c
We were looking for a way to determine if the OS is a guest OS or not.
However, I can see that this is a ARM64 specific API and so probably the
above are only compiled for ARM64. Interestingly, the AMD driver
implements the following ...
static inline bool is_virtual_machine(void)
{
#if defined(CONFIG_X86)
return boot_cpu_has(X86_FEATURE_HYPERVISOR);
#elif defined(CONFIG_ARM64)
return !is_kernel_in_hyp_mode();
#else
return false;
#endif
}
- My own tegra186 HW doesn't have VHE, since it is ARMv8.0, and this
helper will always return 'false'. How could this result in
something that still works? Can I get a free CPU upgrade?
I thought this API just checks to see if we are in EL2?
- If you assign this device to a VM and that the hypervisor doesn't
correctly virtualise it, then it is a different device and you
should simply advertise it something else. Or even better, fix your
hypervisor.
Sumit can add some more details on why we don't completely disable the
device for guest OSs.
Jon
--
nvpublic
