Commit 0aa6b90e authored by Ashish Kalra's avatar Ashish Kalra Committed by Sean Christopherson
Browse files

KVM: SVM: Add support for allowing zero SEV ASIDs 



Some BIOSes allow the end user to set the minimum SEV ASID value
(CPUID 0x8000001F_EDX) to be greater than the maximum number of
encrypted guests, or maximum SEV ASID value (CPUID 0x8000001F_ECX)
in order to dedicate all the SEV ASIDs to SEV-ES or SEV-SNP.

The SEV support, as coded, does not handle the case where the minimum
SEV ASID value can be greater than the maximum SEV ASID value.
As a result, the following confusing message is issued:

[   30.715724] kvm_amd: SEV enabled (ASIDs 1007 - 1006)

Fix the support to properly handle this case.

Fixes: 916391a2 ("KVM: SVM: Add support for SEV-ES capability in KVM")
Suggested-by: default avatarSean Christopherson <seanjc@google.com>
Signed-off-by: default avatarAshish Kalra <ashish.kalra@amd.com>
Cc: stable@vger.kernel.org
Acked-by: default avatarTom Lendacky <thomas.lendacky@amd.com>
Link: https://lore.kernel.org/r/20240104190520.62510-1-Ashish.Kalra@amd.com
Link: https://lore.kernel.org/r/20240131235609.4161407-4-seanjc@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 466eec4a

arch/x86/kvm/svm/sev.c

+19 −10
Original line number Diff line number Diff line
@@ -144,10 +144,21 @@ static void sev_misc_cg_uncharge(struct kvm_sev_info *sev) 


static int sev_asid_new(struct kvm_sev_info *sev)

{

	unsigned int asid, min_asid, max_asid;

	/*

	 * SEV-enabled guests must use asid from min_sev_asid to max_sev_asid.

	 * SEV-ES-enabled guest can use from 1 to min_sev_asid - 1.

	 * Note: min ASID can end up larger than the max if basic SEV support is

	 * effectively disabled by disallowing use of ASIDs for SEV guests.

	 */

	unsigned int min_asid = sev->es_active ? 1 : min_sev_asid;

	unsigned int max_asid = sev->es_active ? min_sev_asid - 1 : max_sev_asid;

	unsigned int asid;

	bool retry = true;

	int ret;



	if (min_asid > max_asid)

		return -ENOTTY;



	WARN_ON(sev->misc_cg);

	sev->misc_cg = get_current_misc_cg();

	ret = sev_misc_cg_try_charge(sev);
@@ -159,12 +170,6 @@ static int sev_asid_new(struct kvm_sev_info *sev) 


	mutex_lock(&sev_bitmap_lock);



	/*

	 * SEV-enabled guests must use asid from min_sev_asid to max_sev_asid.

	 * SEV-ES-enabled guest can use from 1 to min_sev_asid - 1.

	 */

	min_asid = sev->es_active ? 1 : min_sev_asid;

	max_asid = sev->es_active ? min_sev_asid - 1 : max_sev_asid;

again:

	asid = find_next_zero_bit(sev_asid_bitmap, max_asid + 1, min_asid);

	if (asid > max_asid) {
@@ -2234,8 +2239,10 @@ void __init sev_hardware_setup(void) 
		goto out;

	}



	if (min_sev_asid <= max_sev_asid) {

		sev_asid_count = max_sev_asid - min_sev_asid + 1;

		WARN_ON_ONCE(misc_cg_set_capacity(MISC_CG_RES_SEV, sev_asid_count));

	}

	sev_supported = true;



	/* SEV-ES support requested? */
@@ -2266,7 +2273,9 @@ void __init sev_hardware_setup(void) 
out:

	if (boot_cpu_has(X86_FEATURE_SEV))

		pr_info("SEV %s (ASIDs %u - %u)\n",

			sev_supported ? "enabled" : "disabled",

			sev_supported ? min_sev_asid <= max_sev_asid ? "enabled" :

								       "unusable" :

								       "disabled",

			min_sev_asid, max_sev_asid);

	if (boot_cpu_has(X86_FEATURE_SEV_ES))

		pr_info("SEV-ES %s (ASIDs %u - %u)\n",