Re: [PATCH 40/70] x86/sev-es: Setup per-cpu GHCBs for the runtime handler

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On 4/14/20 2:03 PM, Mike Stunes wrote:
On Mar 19, 2020, at 2:13 AM, Joerg Roedel <joro@xxxxxxxxxx> wrote:

From: Tom Lendacky <thomas.lendacky@xxxxxxx>

The runtime handler needs a GHCB per CPU. Set them up and map them
unencrypted.

Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
Signed-off-by: Joerg Roedel <jroedel@xxxxxxx>
---
arch/x86/include/asm/mem_encrypt.h |  2 ++
arch/x86/kernel/sev-es.c           | 28 +++++++++++++++++++++++++++-
arch/x86/kernel/traps.c            |  3 +++
3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/sev-es.c b/arch/x86/kernel/sev-es.c
index c17980e8db78..4bf5286310a0 100644
--- a/arch/x86/kernel/sev-es.c
+++ b/arch/x86/kernel/sev-es.c
@@ -197,6 +203,26 @@ static bool __init sev_es_setup_ghcb(void)
	return true;
}

+void sev_es_init_ghcbs(void)
+{
+	int cpu;
+
+	if (!sev_es_active())
+		return;
+
+	/* Allocate GHCB pages */
+	ghcb_page = __alloc_percpu(sizeof(struct ghcb), PAGE_SIZE);
+
+	/* Initialize per-cpu GHCB pages */
+	for_each_possible_cpu(cpu) {
+		struct ghcb *ghcb = (struct ghcb *)per_cpu_ptr(ghcb_page, cpu);
+
+		set_memory_decrypted((unsigned long)ghcb,
+				     sizeof(*ghcb) >> PAGE_SHIFT);
+		memset(ghcb, 0, sizeof(*ghcb));
+	}
+}
+

set_memory_decrypted needs to check the return value. I see it
consistently return ENOMEM. I've traced that back to split_large_page
in arch/x86/mm/pat/set_memory.c.

At that point the guest won't be able to communicate with the hypervisor, too. Maybe we should BUG() here to terminate further processing?

Thanks,
Tom





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