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[PATCH v3 24/28] arm64/sve: KVM: Hide SVE from CPU features exposed to guests
- From: Dave Martin <Dave dot Martin at arm dot com>
- To: linux-arm-kernel at lists dot infradead dot org
- Cc: Catalin Marinas <catalin dot marinas at arm dot com>, Will Deacon <will dot deacon at arm dot com>, Ard Biesheuvel <ard dot biesheuvel at linaro dot org>, Alex Bennée <alex dot bennee at linaro dot org>, Szabolcs Nagy <szabolcs dot nagy at arm dot com>, Richard Sandiford <richard dot sandiford at arm dot com>, Okamoto Takayuki <tokamoto at jp dot fujitsu dot com>, kvmarm at lists dot cs dot columbia dot edu, libc-alpha at sourceware dot org, linux-arch at vger dot kernel dot org, Marc Zyngier <marc dot zyngier at arm dot com>
- Date: Tue, 10 Oct 2017 19:38:41 +0100
- Subject: [PATCH v3 24/28] arm64/sve: KVM: Hide SVE from CPU features exposed to guests
- Authentication-results: sourceware.org; auth=none
- References: <1507660725-7986-1-git-send-email-Dave.Martin@arm.com>
KVM guests cannot currently use SVE, because SVE is always
configured to trap to EL2.
However, a guest that sees SVE reported as present in
ID_AA64PFR0_EL1 may legitimately expect that SVE works and try to
use it. Instead of working, the guest will receive an injected
undef exception, which may cause the guest to oops or go into a
spin.
To avoid misleading the guest into believing that SVE will work,
this patch masks out the SVE field from ID_AA64PFR0_EL1 when a
guest attempts to read this register. No support is explicitly
added for ID_AA64ZFR0_EL1 either, so that is still emulated as
reading as zero, which is consistent with SVE not being
implemented.
This is a temporary measure, and will be removed in a later series
when full KVM support for SVE is implemented.
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
---
arch/arm64/kvm/sys_regs.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index b1f7552..a0ee9b0 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -23,6 +23,7 @@
#include <linux/bsearch.h>
#include <linux/kvm_host.h>
#include <linux/mm.h>
+#include <linux/printk.h>
#include <linux/uaccess.h>
#include <asm/cacheflush.h>
@@ -897,8 +898,17 @@ static u64 read_id_reg(struct sys_reg_desc const *r, bool raz)
{
u32 id = sys_reg((u32)r->Op0, (u32)r->Op1,
(u32)r->CRn, (u32)r->CRm, (u32)r->Op2);
+ u64 val = raz ? 0 : read_sanitised_ftr_reg(id);
- return raz ? 0 : read_sanitised_ftr_reg(id);
+ if (id == SYS_ID_AA64PFR0_EL1) {
+ if (val & (0xfUL << ID_AA64PFR0_SVE_SHIFT))
+ pr_err_once("kvm [%i]: SVE unsupported for guests, suppressing\n",
+ task_pid_nr(current));
+
+ val &= ~(0xfUL << ID_AA64PFR0_SVE_SHIFT);
+ }
+
+ return val;
}
/* cpufeature ID register access trap handlers */
--
2.1.4