From: Ashish Kalra <[email protected]>
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 <[email protected]>
Signed-off-by: Ashish Kalra <[email protected]>
Cc: [email protected]
---
arch/x86/kvm/svm/sev.c | 40 ++++++++++++++++++++++++----------------
1 file changed, 24 insertions(+), 16 deletions(-)
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 4900c078045a..2112c94bac76 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -143,8 +143,20 @@ static void sev_misc_cg_uncharge(struct kvm_sev_info *sev)
static int sev_asid_new(struct kvm_sev_info *sev)
{
- int asid, min_asid, max_asid, ret;
+ /*
+ * 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();
@@ -157,12 +169,6 @@ 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) {
@@ -246,21 +252,20 @@ static void sev_unbind_asid(struct kvm *kvm, unsigned int handle)
static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
{
struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
- int asid, ret;
+ int ret;
if (kvm->created_vcpus)
return -EINVAL;
- ret = -EBUSY;
if (unlikely(sev->active))
- return ret;
+ return -EINVAL;
sev->active = true;
sev->es_active = argp->id == KVM_SEV_ES_INIT;
- asid = sev_asid_new(sev);
- if (asid < 0)
+ ret = sev_asid_new(sev);
+ if (ret < 0)
goto e_no_asid;
- sev->asid = asid;
+ sev->asid = ret;
ret = sev_platform_init(&argp->error);
if (ret)
@@ -2229,8 +2234,10 @@ 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? */
@@ -2261,7 +2268,8 @@ 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",
--
2.34.1
On 1/4/24 13:05, Ashish Kalra wrote:
> From: Ashish Kalra <[email protected]>
>
> 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 <[email protected]>
> Signed-off-by: Ashish Kalra <[email protected]>
> Cc: [email protected]
One minor comment below that could maybe be done when merging vs sending a
another version? Otherwise...
Acked-by: Tom Lendacky <[email protected]>
> ---
> arch/x86/kvm/svm/sev.c | 40 ++++++++++++++++++++++++----------------
> 1 file changed, 24 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index 4900c078045a..2112c94bac76 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -143,8 +143,20 @@ static void sev_misc_cg_uncharge(struct kvm_sev_info *sev)
>
> static int sev_asid_new(struct kvm_sev_info *sev)
> {
> - int asid, min_asid, max_asid, ret;
> + /*
> + * 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();
> @@ -157,12 +169,6 @@ 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) {
> @@ -246,21 +252,20 @@ static void sev_unbind_asid(struct kvm *kvm, unsigned int handle)
> static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
> {
> struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> - int asid, ret;
> + int ret;
>
> if (kvm->created_vcpus)
> return -EINVAL;
>
> - ret = -EBUSY;
> if (unlikely(sev->active))
> - return ret;
> + return -EINVAL;
>
> sev->active = true;
> sev->es_active = argp->id == KVM_SEV_ES_INIT;
> - asid = sev_asid_new(sev);
> - if (asid < 0)
> + ret = sev_asid_new(sev);
> + if (ret < 0)
> goto e_no_asid;
> - sev->asid = asid;
> + sev->asid = ret;
>
> ret = sev_platform_init(&argp->error);
> if (ret)
> @@ -2229,8 +2234,10 @@ 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? */
> @@ -2261,7 +2268,8 @@ 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",
Just a nit with the alignment, it would look better if the ":" was lined
up under the first "?".
Thanks,
Tom
> min_sev_asid, max_sev_asid);
> if (boot_cpu_has(X86_FEATURE_SEV_ES))
> pr_info("SEV-ES %s (ASIDs %u - %u)\n",
On Thu, Jan 04, 2024, Ashish Kalra wrote:
> From: Ashish Kalra <[email protected]>
>
> 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 <[email protected]>
> Signed-off-by: Ashish Kalra <[email protected]>
> Cc: [email protected]
> ---
> arch/x86/kvm/svm/sev.c | 40 ++++++++++++++++++++++++----------------
This should be ~3 patches:
1. Convert ASID variables/params to unsigned integers.
2. Return -EINVAL instead of -EBUSY
3. The actual fix here
E.g if #2 breaks userspace (extremely unlikely) then bisection should point at
exactly that, not at a commit with a whole pile of unrelated things going on.
I'll send a v4, #1 should also be accompanied by a cleanup of sev_asid_new() to
not multiplex the ASID with the return code. It can simply set sev->asid directly,
which as a bonus makes sev_asid_new() and sev_asid_free() more symmetric.