| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <alpine.DEB.2.22.394.2502111728560.619090@ubuntu-linux-20-04-desktop>
Date: Tue, 11 Feb 2025 17:30:50 -0800 (PST)
From: Stefano Stabellini <sstabellini@...nel.org>
To: Juergen Gross <jgross@...e.com>
cc: linux-kernel@...r.kernel.org, x86@...nel.org, iommu@...ts.linux.dev,
Stefano Stabellini <sstabellini@...nel.org>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>,
Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
xen-devel@...ts.xenproject.org
Subject: Re: [PATCH 2/2] xen/swiotlb: don't destroy contiguous region in all
cases
On Tue, 11 Feb 2025, Juergen Gross wrote:
> In case xen_swiotlb_alloc_coherent() needed to create a contiguous
> region only for other reason than the memory not being compliant with
> the device's DMA mask, there is no reason why this contiguous region
> should be destroyed by xen_swiotlb_free_coherent() later. Destroying
> this region should be done only, if the memory of the region was
> allocated with more stringent placement requirements than the memory
> it did replace.
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
> arch/x86/include/asm/xen/swiotlb-xen.h | 5 +++--
> arch/x86/xen/mmu_pv.c | 18 ++++++++++++------
> drivers/xen/swiotlb-xen.c | 11 +++++++----
> 3 files changed, 22 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/include/asm/xen/swiotlb-xen.h b/arch/x86/include/asm/xen/swiotlb-xen.h
> index abde0f44df57..a353f20c7e79 100644
> --- a/arch/x86/include/asm/xen/swiotlb-xen.h
> +++ b/arch/x86/include/asm/xen/swiotlb-xen.h
> @@ -4,8 +4,9 @@
>
> int xen_swiotlb_fixup(void *buf, unsigned long nslabs);
> int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
> - unsigned int address_bits,
> - dma_addr_t *dma_handle);
> + unsigned int address_bits,
> + dma_addr_t *dma_handle,
> + unsigned int *address_bits_in);
> void xen_destroy_contiguous_region(phys_addr_t pstart, unsigned int order);
>
> #endif /* _ASM_X86_SWIOTLB_XEN_H */
> diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
> index 2c70cd35e72c..fb586238f7c4 100644
> --- a/arch/x86/xen/mmu_pv.c
> +++ b/arch/x86/xen/mmu_pv.c
> @@ -2208,19 +2208,22 @@ void __init xen_init_mmu_ops(void)
> static unsigned long discontig_frames[1<<MAX_CONTIG_ORDER];
>
> #define VOID_PTE (mfn_pte(0, __pgprot(0)))
> -static void xen_zap_pfn_range(unsigned long vaddr, unsigned int order,
> - unsigned long *in_frames,
> - unsigned long *out_frames)
> +static int xen_zap_pfn_range(unsigned long vaddr, unsigned int order,
> + unsigned long *in_frames,
> + unsigned long *out_frames)
> {
> int i;
> + u64 address_bits = 0;
> struct multicall_space mcs;
>
> xen_mc_batch();
> for (i = 0; i < (1UL<<order); i++, vaddr += PAGE_SIZE) {
> mcs = __xen_mc_entry(0);
>
> - if (in_frames)
> + if (in_frames) {
> in_frames[i] = virt_to_mfn((void *)vaddr);
> + address_bits |= in_frames[i] << PAGE_SHIFT;
> + }
>
> MULTI_update_va_mapping(mcs.mc, vaddr, VOID_PTE, 0);
> __set_phys_to_machine(virt_to_pfn((void *)vaddr), INVALID_P2M_ENTRY);
> @@ -2229,6 +2232,8 @@ static void xen_zap_pfn_range(unsigned long vaddr, unsigned int order,
> out_frames[i] = virt_to_pfn((void *)vaddr);
> }
> xen_mc_issue(0);
> +
> + return fls64(address_bits);
> }
>
> /*
> @@ -2321,7 +2326,8 @@ static int xen_exchange_memory(unsigned long extents_in, unsigned int order_in,
>
> int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
> unsigned int address_bits,
> - dma_addr_t *dma_handle)
> + dma_addr_t *dma_handle,
> + unsigned int *address_bits_in)
> {
> unsigned long *in_frames = discontig_frames, out_frame;
> unsigned long flags;
> @@ -2336,7 +2342,7 @@ int xen_create_contiguous_region(phys_addr_t pstart, unsigned int order,
> spin_lock_irqsave(&xen_reservation_lock, flags);
>
> /* 1. Zap current PTEs, remembering MFNs. */
> - xen_zap_pfn_range(vstart, order, in_frames, NULL);
> + *address_bits_in = xen_zap_pfn_range(vstart, order, in_frames, NULL);
>
> /* 2. Get a new contiguous memory extent. */
> out_frame = virt_to_pfn((void *)vstart);
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index 26c62e0d34e9..3f3724f53914 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -118,6 +118,7 @@ int xen_swiotlb_fixup(void *buf, unsigned long nslabs)
> int rc;
> unsigned int order = get_order(IO_TLB_SEGSIZE << IO_TLB_SHIFT);
> unsigned int i, dma_bits = order + PAGE_SHIFT;
> + unsigned int dummy;
> dma_addr_t dma_handle;
> phys_addr_t p = virt_to_phys(buf);
>
> @@ -129,7 +130,7 @@ int xen_swiotlb_fixup(void *buf, unsigned long nslabs)
> do {
> rc = xen_create_contiguous_region(
> p + (i << IO_TLB_SHIFT), order,
> - dma_bits, &dma_handle);
> + dma_bits, &dma_handle, &dummy);
> } while (rc && dma_bits++ < MAX_DMA_BITS);
> if (rc)
> return rc;
> @@ -144,6 +145,7 @@ xen_swiotlb_alloc_coherent(struct device *dev, size_t size,
> dma_addr_t *dma_handle, gfp_t flags, unsigned long attrs)
> {
> u64 dma_mask = dev->coherent_dma_mask;
> + unsigned int address_bits = fls64(dma_mask), address_bits_in;
> int order = get_order(size);
> phys_addr_t phys;
> void *ret;
> @@ -160,10 +162,11 @@ xen_swiotlb_alloc_coherent(struct device *dev, size_t size,
> if (*dma_handle + size - 1 > dma_mask ||
> range_straddles_page_boundary(phys, size) ||
> range_requires_alignment(phys, size)) {
> - if (xen_create_contiguous_region(phys, order, fls64(dma_mask),
> - dma_handle) != 0)
> + if (xen_create_contiguous_region(phys, order, address_bits,
> + dma_handle, &address_bits_in))
> goto out_free_pages;
> - SetPageXenRemapped(virt_to_page(ret));
> + if (address_bits_in > address_bits)
> + SetPageXenRemapped(virt_to_page(ret));
This has the unfortunate side effect of making "PageXenRemapped"
unreliable as an indicator of whether a page has been remapped. A page
could still be remapped without the "PageXenRemapped" bit being set.
I recommend adding an in-code comment to clarify this behavior.
> }
>
> memset(ret, 0, size);
> --
> 2.43.0
>
Powered by blists - more mailing lists