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hypervisor: mshv: handle Special Debug Print VMG exit

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Add handling for GHCB_INFO_SPECIAL_DBGPRINT VMG exit in the SEV-SNP
guest exit handler. This exit occurs when the guest sends debug print
requests through the GHCB interface.

Without this handler, SEV-SNP guests fail to boot when debug output
is triggered, such as when a debugger is attached to the guest image.

The handler acknowledges the exit without printing to avoid performance
degradation from frequent debug print requests.

Signed-off-by: Muminul Islam <muislam@microsoft.com>
This commit is contained in:
Muminul Islam 2026-02-13 12:18:10 -08:00 • committed by Rob Bradford
parent 30c86d5999
commit ff4c8f7480
1 changed files with 13 additions and 0 deletions
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13
hypervisor/src/mshv/mod.rs
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@ -873,6 +873,19 @@ impl cpu::Vcpu for MshvVcpu {
assert!(info.header.intercept_access_type == HV_INTERCEPT_ACCESS_EXECUTE as u8);
match ghcb_op {
GHCB_INFO_SPECIAL_DBGPRINT => {
// Handle debug print from guest
// The guest sends a character to print via GHCB data
// Sample debug print implementation that only prints ASCII characters and ignores the rest
// let char_to_print = (ghcb_data & 0xFF) as u8;
// if char_to_print.is_ascii() {
// debug!("'{}'", char_to_print as char);
// }
// Not printing the character to slow down the guest a bit,
// as these debug prints can be very frequent.
// In real implementation, we might want to buffer these characters and
// print them out together or implement some rate limiting.]
}
GHCB_INFO_HYP_FEATURE_REQUEST => {
// Pre-condition: GHCB data must be zero
assert!(ghcb_data == 0);