linux-kernel - [RFC PATCH v2 07/35] KVM: selftests: Return an unused GHCB from the pool

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Message-ID: <20250923050942.206116-8-Neeraj.Upadhyay@amd.com>
Date: Tue, 23 Sep 2025 10:39:14 +0530
From: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
To: <kvm@...r.kernel.org>, <seanjc@...gle.com>, <pbonzini@...hat.com>
CC: <linux-kernel@...r.kernel.org>, <Thomas.Lendacky@....com>,
	<nikunj@....com>, <Santosh.Shukla@....com>, <Vasant.Hegde@....com>,
	<Suravee.Suthikulpanit@....com>, <bp@...en8.de>, <David.Kaplan@....com>,
	<huibo.wang@....com>, <naveen.rao@....com>, <pgonda@...gle.com>,
	<linux-kselftest@...r.kernel.org>, <shuah@...nel.org>, <tiala@...rosoft.com>
Subject: [RFC PATCH v2 07/35] KVM: selftests: Return an unused GHCB from the pool

The ghcb_alloc() function in the SEV selftest library always returned
the first GHCB from the pool, regardless of whether it was already in
use. In a multi-vCPU test, this causes all vCPUs to share and corrupt
the same GHCB, leading to unpredictable test failures.

Modify ghcb_alloc() to iterate through the pool and return the first
entry that is not currently marked as in_use. Mark the selected entry
as in use before returning it to prevent other vCPUs from allocating it.

Additionally, correct a minor bug in the memset call which was
incorrectly taking the address of the ghcb pointer instead of using
the pointer value itself.

This ensures that each vCPU in a test gets its own unique GHCB, allowing
multi-threaded SEV-ES tests to run correctly.

Signed-off-by: Neeraj Upadhyay <Neeraj.Upadhyay@....com>
---
 tools/testing/selftests/kvm/lib/x86/sev.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/lib/x86/sev.c b/tools/testing/selftests/kvm/lib/x86/sev.c
index de36a6c93839..3090a6518066 100644
--- a/tools/testing/selftests/kvm/lib/x86/sev.c
+++ b/tools/testing/selftests/kvm/lib/x86/sev.c
@@ -68,7 +68,6 @@ static void sev_es_terminate(void)

 static struct ghcb_entry *ghcb_alloc(void)
 {
-	return &ghcb_pool->ghcbs[0];
 	struct ghcb_entry *entry;
 	struct ghcb *ghcb;
 	int i;
@@ -81,7 +80,7 @@ static struct ghcb_entry *ghcb_alloc(void)
 			entry = &ghcb_pool->ghcbs[i];
 			ghcb = &entry->ghcb;

-			memset(&ghcb, 0, sizeof(*ghcb));
+			memset(ghcb, 0, sizeof(*ghcb));
 			ghcb->ghcb_usage = 0;
 			ghcb->protocol_version = 1;

-- 
2.34.1