Patch "KVM: SVM: Add support for allowing zero SEV ASIDs" has been added to the 6.6-stable tree

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This is a note to let you know that I've just added the patch titled

    KVM: SVM: Add support for allowing zero SEV ASIDs

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kvm-svm-add-support-for-allowing-zero-sev-asids.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 0202c1d64303b5c4f85e0358008fc049d3df5bb0
Author: Ashish Kalra <ashish.kalra@xxxxxxx>
Date:   Wed Jan 31 15:56:08 2024 -0800

    KVM: SVM: Add support for allowing zero SEV ASIDs
    
    [ Upstream commit 0aa6b90ef9d75b4bd7b6d106d85f2a3437697f91 ]
    
    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: 916391a2d1dc ("KVM: SVM: Add support for SEV-ES capability in KVM")
    Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
    Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
    Cc: stable@xxxxxxxxxxxxxxx
    Acked-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
    Link: https://lore.kernel.org/r/20240104190520.62510-1-Ashish.Kalra@xxxxxxx
    Link: https://lore.kernel.org/r/20240131235609.4161407-4-seanjc@xxxxxxxxxx
    Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index ea68a08cc89c2..c5845f31c34dc 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -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) {
@@ -2236,8 +2241,10 @@ void __init sev_hardware_setup(void)
 		goto out;
 	}
 
-	sev_asid_count = max_sev_asid - min_sev_asid + 1;
-	WARN_ON_ONCE(misc_cg_set_capacity(MISC_CG_RES_SEV, sev_asid_count));
+	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? */
@@ -2268,7 +2275,9 @@ 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",




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