From 64b21662b1b1619b7b411365aa83ec7fca9edeb4 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Marek=20Marczykowski-G=C3=B3recki?= Date: Tue, 30 Apr 2024 08:31:01 +0200 Subject: [PATCH] x86/msi: passthrough all MSI-X vector ctrl writes to device model MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit QEMU needs to know whether clearing maskbit of a vector is really clearing, or was already cleared before. Currently Xen sends only clearing that bit to the device model, but not setting it, so QEMU cannot detect it. Because of that, QEMU is working this around by checking via /dev/mem, but that isn't the proper approach. Give all necessary information to QEMU by passing all ctrl writes, including masking a vector. Advertise the new behavior via XENVER_get_features, so QEMU can know it doesn't need to access /dev/mem anymore. While this commit doesn't move the whole maskbit handling to QEMU (as discussed on xen-devel as one of the possibilities), it is a necessary first step anyway. Including telling QEMU it will get all the required information to do so. The actual implementation would need to include: - a hypercall for QEMU to control just maskbit (without (re)binding the interrupt again - a method for QEMU to tell Xen it will actually do the work Those are not part of this series. Signed-off-by: Marek Marczykowski-Górecki Reviewed-by: Jan Beulich Acked-by: Roger Pau Monné --- xen/arch/x86/hvm/vmsi.c | 19 ++++++++++++++----- xen/common/kernel.c | 1 + xen/include/public/features.h | 8 ++++++++ 3 files changed, 23 insertions(+), 5 deletions(-) diff --git a/xen/arch/x86/hvm/vmsi.c b/xen/arch/x86/hvm/vmsi.c index adbac965f9..9999179837 100644 --- a/xen/arch/x86/hvm/vmsi.c +++ b/xen/arch/x86/hvm/vmsi.c @@ -283,8 +283,8 @@ static int msixtbl_write(struct vcpu *v, unsigned long address, unsigned long flags; struct irq_desc *desc; - if ( (len != 4 && len != 8) || (address & (len - 1)) ) - return r; + if ( !IS_ALIGNED(address, len) ) + return X86EMUL_OKAY; rcu_read_lock(&msixtbl_rcu_lock); @@ -345,8 +345,7 @@ static int msixtbl_write(struct vcpu *v, unsigned long address, unlock: spin_unlock_irqrestore(&desc->lock, flags); - if ( len == 4 ) - r = X86EMUL_OKAY; + r = X86EMUL_OKAY; out: rcu_read_unlock(&msixtbl_rcu_lock); @@ -357,7 +356,17 @@ static int cf_check _msixtbl_write( const struct hvm_io_handler *handler, uint64_t address, uint32_t len, uint64_t val) { - return msixtbl_write(current, address, len, val); + /* Ignore invalid length or unaligned writes. */ + if ( (len != 4 && len != 8) || !IS_ALIGNED(address, len) ) + return X86EMUL_OKAY; + + /* + * This function returns X86EMUL_UNHANDLEABLE even if write is properly + * handled, to propagate it to the device model (so it can keep its + * internal state in sync). + */ + msixtbl_write(current, address, len, val); + return X86EMUL_UNHANDLEABLE; } static bool cf_check msixtbl_range( diff --git a/xen/common/kernel.c b/xen/common/kernel.c index 08dbaa2a05..b44b2439ca 100644 --- a/xen/common/kernel.c +++ b/xen/common/kernel.c @@ -637,6 +637,7 @@ long do_xen_version(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg) fi.submap |= (1U << XENFEAT_hvm_safe_pvclock) | (1U << XENFEAT_hvm_callback_vector) | (has_pirq(d) ? (1U << XENFEAT_hvm_pirqs) : 0); + fi.submap |= (1U << XENFEAT_dm_msix_all_writes); #endif if ( !paging_mode_translate(d) || is_domain_direct_mapped(d) ) fi.submap |= (1U << XENFEAT_direct_mapped); diff --git a/xen/include/public/features.h b/xen/include/public/features.h index 4437f25d25..8801930947 100644 --- a/xen/include/public/features.h +++ b/xen/include/public/features.h @@ -120,6 +120,14 @@ #define XENFEAT_runstate_phys_area 18 #define XENFEAT_vcpu_time_phys_area 19 +/* + * If set, Xen will passthrough all MSI-X vector ctrl writes to device model, + * not only those unmasking an entry. This allows device model to properly keep + * track of the MSI-X table without having to read it from the device behind + * Xen's backs. This information is relevant only for device models. + */ +#define XENFEAT_dm_msix_all_writes 20 + #define XENFEAT_NR_SUBMAPS 1 #endif /* __XEN_PUBLIC_FEATURES_H__ */